Rear main seal isn't a difficult job and ain't vehicle specific enough to ship outta state. Case of beer and a mechanic friend can get it done. Either way a local reputable mechanic shop should get it done easy.
Sounds like cam sensor cap not adjusted right(I'm guessing you have LED cap) try other known good one. Recheck plug wires, I put a new set on and one was bad, had same symptoms.
He sent me that crap too, haven't met too many turbobuick Aussie owners. Between parts and helping a Nigerian Prince reclaim his throne, I can't afford to fall for that old banna in the tailpipe gag!