This is just a long shot, but sometimes oil leaks through the threaded holes located just above the spark plugs, that the valve ball stud adjusters are seated in. It can look like the leak is coming from the spark plugs. You can check higher up the head, to see if maybe the fluid is coming from above (one of) the plugs. You could also try re-torqueing the head, never hurts. Here's a procedure for that:
Before you retorque, make sure there's no pressure in the cooling system. Loosen the overflow canister cap and re-fit. The sequence of the bolts is from the inside out, there's a diagram in the Haynes manual. Loosen each bolt for at least a half a turn, then tighten to 60 lbs (double check your engine specs to be sure). Use a bit of oil on the threads and washers so they screw down evenly. It's easy to do with a relatively long 10 mm Allen key. Don't forget the bolts in the timing chain housing. Modern head gaskets are said to not need re-tightening, but do it anyway to be sure. After you do the bolts, check the valve clearances.
Cees
white 1969 280 SL