Finding an oily bottom spark plug is not necessarily a problem, but oily top and bottom plugs typically indicate that excessive oil is leaking past the rings.
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If there are no signs of ring damage, the compressions are within spec, and the oil usage is within the manufacturer?s spec, I would be hesitant to recommend pulling a cylinder based on oil consumption alone
I had an O320 160 hp powered 4 for 4 years and 450 hrs. The oil consumption was 1 qt every 12-15 hrs. After about 15 hrs it would start to run rough during the runup. Usually the #4 bottom plug but occasionally a different bottom plug was fouled. Often the #4 plug was a little oily. Cpmpressions were all in the mid 70's. I put 37BY's in the bottom and went from 15 to 100 hr cleanings with no issues. Always leaned in cruise and on the ground. Still running the same today with a new owner. FWIW.
Al
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