Crack in head or bad gasket won't cause oil fouled spark plugs, it will cause other problems but not that problem.
Compression test will tell you if valve timing, rings and valve seats are OK, valve guide seals are not tested, as they are outside of the cylinder.
And a compression test result isn't very useful unless several cylinders are tested, you need a baseline.
A vacuum gauge is a nice, and inexpensive tool, to have.
A fast flutter of vacuum gauge needle at warm idle would indicate worn valve guide seals.
Would one worn seal burn a quart of oil in 250 miles, no probably not, but I have never seen one worn seal, lol, you just may have one that is leaking more oil, but all would be leaking some oil.
And because of the physics of motion the oil in the valve covers tends to pool at the rear of the head, where #3 and #6 valves are located, so higher possible oil flow into those seals.
Usually valve guide seals will crack if allowed to dry out, this happens if engine sits for long periods.
100k on a '94 would mean it was sitting for long periods.
Low mile vehicles are a pain in this respect, seals dry out and crack, rear main is the bad one.
There are products like Lucas oil treatment that swell rubber seals and soften them, you could try some and see if oil consumption goes down, this would indicate worn seals, since rings would not be effected.
Valve guide seals can be changed without removing the heads.
Last edited by RonD; 02-24-2014 at 10:38 AM.