I would have to cry foul on that one too. I have done more 850/S-70 transmissions and rear main seals than I can remember and I have never seen a harness take a dump from it. Especially a 6 year old harness!?!? Is this a Volvo shop that did the work? I would have to ask the to explain just exactly what the nature of the defect is, where it is, and then I would need to see it in person. The harness does run right across the top of the bell housing but it is housed in a hard plastic sheath and really should not have any problems with deterioration, especially this early in the game. Even the 200 series harnsesses that everyone and their brother has done did not start to show signs of deterioration until they were 8-10 years old and some went much longer than that. Bottom line is you drove the car in and now it won't start and run after they put a rear seal in it, they need to physically show what the deal with your harness is and explain to your satifaction why it is not their baby. Good Luck, 'cause you're going to need it.