The guides may be done. Typically the oem clearance is .001 to .003, but cannot be measured with feeler gauges. They are measured with micrometers; inside and outside and then computed. To say you slipped a feeler down the guide beside the stem, indicates the actual clearance may be quite a bit more than the gauge thickness, as the feeler gauge will not conform to the clearance space, and then there's the feeler aspect of feeler gauges. As in just how hard should it be to push/pull the valve against the drag of the feeler.These are not 4 inch pistons.
So,either procure the correct tools or sub the measuring out to a headshop.There is a good chance that the guides are less than the service limit, in which case it would be a judgement call, as to weather or not to replace them. But since the heads are already off(are they off?),and indicating signs of distress, hmmmm
To answer the question about oil getting by, The short answer is yes, as you have discovered.
Heres the test; Pick a guide and valve.Clean them with a no-residue solvent. If there is carbon on the back, leave it there but make sure it is rid of oil. Assemble them. Pull the valve over and secure it with something so that its not likely to move (like a small bungie-cord). Then put a few drops of very thin oil, like sewing machine oil on the stem, and leave it like that, for an hour or so. When you return look for the oil on the back of the valve head. If you don't see any, I would put more oil on and wait again.
The oil should, by capillary action, creep through the guide and be visible on the back of the valve. No oil means............ probably/possibly, a good seal. Remember, when the engine is running, it can put a pretty good pressure differential across that seal.
