I went to the shop and found out that my crank seal is leaking and leaked oil all over my opti, which was causing the misfire. He said that he can rebuild the opti and that alot of people don't know this and just buy a knew one, is this right? He quoted me around 900 dollars for all this work, full tune up(plugs wires, pcv), crank seal, rebuilt opti, how does this sound to everyone out there?

 

he says he uses all gm dealer parts too

 

GM doesn't sell 'rebuilt' optis, nor any parts FOR it [except cap and rotor]
A lot of people call the cap and rotor a 'rebuild kit'
But ask youself.. what about the BEARING[ that tends to go bad.. and is NOT available, even from NTN] also the rust that no doubt is inside[the EMF shields tend to rust a lot]
Do yourself a favor get a new GM opti for 300 from Jason Cromer, etc..