I've already replied to Sandra in an email, which I think must have just arrived in her mail as she was typing this post. This is some of what I offered:

"Is there anything I can do to help the shrubs at this point so that the leaves regain some life and stop drying and yellowing?" No. There is only one degree of dead. Sorry - couldn't resist that. ;o) The drought response from over-watering involves the formation of a corky layer (abscission layer) where the leaf petiole meets the stem (in the abscission zone). The layer prevents the movement of water (sap) and nutrients through this zone and once formed, the layer cannot be reversed or undone.

"I've read that 1/8 tsp. of Espom salts in a gallon of water [giving the plants just a little of the mixture] might help, or spraying the leaves with seaweed nutrient spray. Would this be a good idea at this point?"

No. Unless you've isolated a MG or a S deficiency. Applying anything in elemental form or in a compound that supplies only a couple of nutrients is far more apt to create problems than resolve them. E.g., adding Mg w/o some attention to the ratio of Ca to Mg can create antagonistic deficiencies of either Ca or K. Also, see comment above - it's not going to make a difference.

There is no pathway into the plant for the organic molecules in seaweed (suspension) sprays, though it does contain a small amount of nutrition in ionic (soluble) form. The organic molecules would need to be broken down into elemental form on the leaf surface and then be carried into the plant via a diffusive pathway, which isn't going to happen (I'll explain if you would like me to). Effective foliar applications are ionic (like Miracle-Gro or other soluble fertilizers) and then they are only marginally effective on a fairly low % of plants. It's almost certainly not a nutritional issue, unless the issue is resultant of over-fertilizing, in which case additional nutrient applications will exacerbate the problem.

"... when I bought these buckthorn plants, they had, and still have, white spots and specks on the leaves ..... Do you have any idea what this might be and what I should do to get rid of it?"

Probably insecticide/fungicide residue - possibly dissolved solids deposits from OH watering or employees wetting foliage when they water. All are pretty common on nursery plants, especially if they're using Daconil as a fungicide. It will disappear with the next flush of foliage, but you'll probably have to live with it until then.

About the salt thing: We might muse that there is some possibility it is salt. Many plants are able to cope with high concentrations of particular or multiple types of ions in the soil by taking them up from the soil solution and then expelling them in concentrated form in a guttative exudate (search guttation). Simplified, this means that salt tolerant plants often employ the strategy of eliminating the salt they take up in a concentrated salt solution they weep through their leaves. Once the solution (exudate) dries, it leaves behind crystalline deposits to be eventually rinsed from the leaves by rain or diluted by dew. These deposits are usually fairly localized & tend to accumulate at particular points where the plant weeps or the exudate collects - leaf-tips, e.g.

I mentioned that I have a Rhamnus frangula 'Aspleniifolia' (fernleaf buckthorn) in my garden, but I've never noticed any stains from exudates that might contain salts on the foliage.

Al