Upload & Sell: On
I definitely wouldn't try to compensate for it by focusing in front or in back of the subject. I'd rather use live view focus / manual focus.
If it's distance shooting though, you might try just using center point / recompose. This shouldn't throw off focus like it might shooting at F1.4 with a very close subject and a fast portrait lens.
I have not used these guys personally (have never had to repair anything, knock on wood), but I've heard nothing but good things about them
Sorry to hear about your frustrations, that's a very expensive lens but I also get the feeling that it's extremely sensitive and complicated gear. If you were nearby you could give mine a test drive, I'm very pleased with my copy and glad I sold my VR1 and didn't buy the Sigma I was looking at - when these are good they're very, very good.