You asked the mechanic the right questions. Some other thoughts/questions i would consider when removing the rear main seal is that they do a thourough check. I had mine done 2 times in 6 weeks. They thought it was the rear main seal only but it turned out to be that + the the lower engine block half. I had oil dripping from the lower engine block too. They then had to remove the lower portion of the engine and re-seal this block with a clear sealer (not the thick blue gunk that Noth American cars use). I think it is important that you ask him if this problem is not fixed after he does the replacement will you have to pay to have this area worked on again. I asked them before they did mine the first time. When they went in the second time i only had to pay for the additional time it would have taken them initially (5 more hours) and not for the entire time (about 13 hours). It saved my at least $800.
likely it is only the seal but it is better to work that scenario out before they get into it a second time and you have no choice.
Good luck.
Jeff W
1994 854 T5
1994 855 T5