[mr0077]

I got a suggestion recently from an old mechanic that has worked like a champ...get your flip-lever spring compressor from Napa for about $25-$30...go by the hardware store and buy about 4 feet of 3/16" to 1/4" cotton clothesline rope (3/16" works better, hell buy 4' of each and use the one you like). Pull all the plugs and the rocker shafts (of course), and on the cylinder you plan to work on, roll the piston about 1/3-1/2 way down the bore, thread as much of the rope as you can into the cylinder through the spark plug hole, gently roll the piston back toward TDC until it pushes the rope up against the bottom of the valves and the cylinder head, and get after it. The rope will keep the valve from dropping into the cylinder, with no need for air, and won't hurt anything. Using air makes me a little uneasy worrying about losing the pressure seal against the valve, and the compressor is noisy. If you do use air, put the transmission in top gear after the piston is at TDC with the E-brake set to keep the air pressure from pushing the piston to BDC.
On your symptoms, though, I agree it is probably guide seals, but usually guide seals do just the opposite, start off blowing a puff when cold and gradually get worse from there.