The labor hours for the O-ring R&R is about 8 hours (so says the local MB dealer)! Whoa!!!
I'm not going to spend that much money if I can do it myself. Anyway, I was also thinking about the tranny stop leak products or just keep adding fluid like LarryB said in other posts. Cheaper to add a quart than pay the dealer. But I'm not sure on the longevity of the O-rings at this stage. It leaks about a tablespoon each day.
Force be with you,