The Stovebolt Site Forums The Shop Area Engine Shop Valve seals are failing.

Those are positive type valve seals. They fit tight over the exposed section of the valve guide, above the the valve spring seat. So they were either damaged as HRL stated, OR, the lift of the aftermarket cam is causing the top spring retainer to contact the top of the valve seal. I would definitely find out what the lift of the cam is. Sometimes you have to cut the top of the valve guides down to create enough clearance for the seals. The other style seal (an umbrella type) installs over the valve stem and rides up and down with the valve. That is the type of seal I installed on my 235. The stock o-ring style seals don't do a very good job of keeping oil out of the valve guides.