I had this same type of experience on a 87SDL a few months ago..In fact it was the next day after I had looked the car over and advised my friend to buy it, as it seemed pretty solid. He had it out the next day, and bingo 1st & 2nd slipped and complained like mad 3rd was ok, and reverse was fine. I replaced the B2 piston & put a spring kit in (a K1, but I might be mistaken,would have to look it up). At any rate, transmission operated much better than before, and has not given any trouble since. Was about 6k miles ago. Makes me wonder how many transmissions have been replaced, when it was just a bum B2 piston..

Bill