The most likely cause of your problem is a dried out root ball. Pot grown rhododendrons are very prone to this - there are many examples on this forum. The light peat based medium used by the grower is very hard to rewet once it dries out. The problem is made worse if at planting the roots are not cut, raked with a cultivator or otherwise unmatted. The best thing to do is to dig up the plant, tease out the roots - don't be afraid to really do this thoroughly - and soak in a bucket until the root mass is wet. Then replant. If you notice signs of wilting over the summer, water at the base of the plant with a slow trickle for 30 to 60 minutes. Don't soak the whole bed. That just makes it harder for the roots to move out of the original medium and into the soil around it. You may have to use the trickle technique again next year, too.

"Special attention" is a pretty subjective term. For instance, full repots that include bare-rooting, root pruning, and a complete change of soil on a regular basis is not "special attention" to me. It's simply a regular part of the program by which I'm able to keep perennials alive (trees are perennials, too) and in a high state of vitality indefinitely. Most growers are not even aware that this is the only way to avoid a steady decline and eventual death of the plant due to the effects of root congestion. This is definitely a cultural consideration that can cause problems that lead to the plant's demise. When it comes to container media, your focus would best be directed to your medium's structure, not it's ability to feed the plant. Trying to build media that are able to feed the plant is fraught with tribulation, because the hydrocarbon chains that organic materials are made of must be broken down to reduce then into elemental or otherwise usable (to the plant) forms. This destroys the soil's ability to hold a favorable ratio of air:water, which results in poor root function/health. Much wiser for the grower to work at ensuring the soil is able to retain its structure for the expected interval between repots, and shoulder the entire burden of providing nutrition. If you aren't fertilizing, you're overlooking a responsibility that belongs to all container gardeners. Lacking adequate nutrition, plants 'steal' any mobile nutrients from other plant parts and use those nutrients to fuel new growth while shedding old growth. This is not a sustainable arrangement and always ends in death of the organism unless the trend is reversed. No organism can use more energy than it can produce for long. You might find information that provides additional insight if you follow the link. Plants require conditions they can tolerate. If they can't, it leads to stress. Stress turns to strain, and the inability to make more food than it is converting to energy and using. This means the plant cannot grow. Growth isn't measured by how many new leaves a plant might produce, it's measured by the increase in dry mass; so, a plant that is putting on new growth while shedding old parts isn't necessarily growing, and plants that aren't growing are dying. I guess the main point I would make is, there's a lot more to growing things efficaciously than bringing them home from the store and watering them when they need it or we get around to it. I look at it from a scientific perspective, and I shun trial and error. Knowledge about soils and how plants work (physiologically) is the propellant by which you can most rapidly advance. Trial and error, essentially stumbling around in the dark is more a tether to bad habits than a method of learning. That's just one person's POV. YMMV Al

I would clean up the weeds and small plants around the trunk and give the tree more space. And then, I would add some fresh and clean top soil or potting soil on top of the roots to cover the roots up, about 1/2 to 1 inch, and sprinkle some water to work the soil into the roots. Air bubbles and empty spaces between roots can kill the root hairs on the roots. The soil will fill up those empty spaces. Root hairs are the main tissue to absorb water and nutrients to the tree. Do not add too much of water as we want to avoid water log and root rot. I avoid using organic top soil or organic potting soil as most of them contain manure or other unknown organic substances, especially when the tree is weak right now. If I have some potting plants, I would move them near the tree to create micro-climate to keep it warm in winter, but not too close. Too close could create too much moisture, which promote fungal growth. I also would not let their branches touching each other to avoid scratching each other to create wounds. Move those potting plants away in other part of the year for fresh air and sun light. I would feed it with half strength of Miracle Gro solution for the tree to reduce the transplanting shock, just for one time at this time. Winter is not its time for fertilizing. Too much of fertilizer will promote new growth, which will be killed by cold weather. I agree with Grant Yang's assessment. Michelia alba is a tropical tree. The tree drops some leaves is responding to the cold weather. The roots of Michelia alba are quite brittle. Once it was planted in about the right level with the ground, do not dig it up again. The roots should not be exposed to the air too. Cover the roots up with clean top soil. Bay Area is in rainy season right now. We do not need to water them unless the top soil is dry by a few sunny days. Good luck. I transplanted my 5 years old Michelia alba from pot to ground 3 years ago. It is under a tall Russian Olive tree. I live in East Bay. It is hot in summer and cold in winter. From time to time, it is quite windy too. I have to stick it to keep it straight. I plan to prune it next year to keep it about 12 feet tall.

I'm not hugely experienced, but that sounds like WAY too much water for a new plant. Also, unless you water is very alkali, acid every time you water is too much as well. Most local hardware stores have soil testers. I would recommend testing the pH of your soil and go from there as far as acidity. I'd also cut back to about 1/4 gallon a day at most unless its consistently over 90 and low humidity. The top of the soil can be a little dry in-between.