I thought you said you had oil in the magneto side? Maybe that was
@Aikaru, swore it was you. My bad, but naw unless the plug is hanging out the oil seep won't really take much compression. I'm thinking you have a gasket leak bro. It's all the classic signs. I even went through it when tuning 'ol red my nitro bike. Turns out for me it was timing, but you are a gasket leak. Runs alright when cold, little dinkin, but alright. Then a few minutes later when it starts to get warm it goes haywire and no two plug readings are the same. You richen it up and it gets worse, you lean it and it won't run. It's a bad gasket somewhere. Only thing it can be besides oh a cracked jug/case/head/etc.
Or did you say something about it dripping oil from the underside? I know I was helping some one that had a bad crank seal. Frogslayer was helping them too, gave some pointers on how to tap the crank seal in.