Please put a location and or zone next to your name so we can help better, as some advise depends upon your location. A North facing window is not enough light for a tree, they need a South facing window to get through the winter. A West window will keep them alive but it's still not enough light. You may have to add lighting to give the plant enough. The white on the stems could be latex sap or mealy bugs, it's hard to tell. The spots look like oedema ( when the plant has too much water in it's stems and leaves and it gets too cold causing cells to burst) Some of the leaves look way too dry also. It could also be accumulated salts causing the brown leaf tips. The next time you water do a full flush. You will probably need help to get it to the shower but give it a really good soak. Do not let the water get too cold. When it's done draining, tilt the pot a few times then move it back. (hopefully to better lighting)

Just keep eye on the healthy leaves. If other leaves stay healthy in 2 or 3 days, then nothing to worry. If the symptoms spread further, maybe soil nutrients deficiency is the cause. No need to cut off any leaves since they still able to do photosynthesis, but if you think remove unhealthy leaves will make you feel better, then go ahead. Seems that you have enough healthy leaves to support plant growth.

Leaves are the plant's power source, and they're not diseased, so removing them just weakens the plant's ability to replace roots that have died due to overwatering. Roots need air for oxygen, so monitor the soil moisture at the bottom of the pot with the dowel test and only water when it comes out dry to the touch. Here's a post by Al from this thread. I guarantee that following this advice will take care of your watering issues and stop any more brown areas. Read the whole thread to really understand what's going on. "The calendar isn't what determines an appropriate watering interval; and you, not the guys at the store where you bought the plant, are in the best position to determine when your plant does or doesn't need watering. When the skewer first comes out dry or almost dry is the appropriate time to water. There ARE some things you can do that will shorten the intervals between necessary waterings, which would mean the plant has a greater fraction of unsaturated soil for a higher % of time, which is decidedly a plus. Follow this link to info on how to deal with water-retentive soils."

Thank you so much for responding (and for talking me off the ledge!) Sorry I wasn't being clear...I have not yet repotted and was waiting until June to do so. I haven't examined the soil closely, but once when I was lifting/transporting the tree to water it, the pot just fell off the plant onto to the ground. it did make some mess but the potting medium pretty much held together in the shape of the pot. So, I'd say at least "old" if not "bad" soil? Should I look at the roots more closely and if so, what am I looking for? (And what would I do if I found it?) If this guy does survive, I will summon up the courage to repot hopefully in Al's 5:1:1 in June if I can manage to find all the right ingredients (been working on that for some time.) Very nervous to repot something this size. I did spray all the other bigger plants in the house and will now do the rest of them (and this one) once a week...thank you! I knew they traveled from plant to plant....but, hitch a ride on me? I might never sleep again knowing that...lol. Also, I haven't fertilized at all--I know I've read somewhere on this Forum that it's good to do a weaker Foliage Pro all year(?) but I wasn't sure if I should just initiate that at this time of year--even at a weaker strength, much less when the plant is stressed? I'm thinking I should wait for new growth to start fertilizing? Thank you, thank you for taking the time to help!!!!