I totally agree that 120k is too few miles for valve seals, but what you describe is classic symptoms for that engine. Google N62 valve seals and search youtube also. I'm a long time hot rodder also, so I'm with you about that it shouldn't need them. No need to pull the heads, guides are usually good, and you will need AGA tool kit N62 Valve Stem Seal Master's Collection | AGA Tools to do this, buy a used set on ebay. If you do pull the valve covers, you may want to remove the 3 red plastic tabs on the exhaust side of the valve cover before installing. They make it way harder to install the cover and prevent it from seating/sealing if you don't get it just right, very difficult with engine in car. Sending you a PM with contact info if you want.