Michael wrote: "...Thanks for your input! Your comments make me want to more attribute my leaks to the fact that my wagon likely sat still 5 months/year here in New England...."
Definitely. MBs are notorious for having seals that are NOT meant to be left unused for long periods. The best thing that you can do for your car is drive it, at least once a month, even in the winter. I can't blame your concern about salt, but pick a day when the roads are clear and take it for a drive. That car (not just the engine, but many suspension parts, too) will last a LOT longer if it doesn't have to endure an annual several-month out-of-service drying-out intervals.