2000 Toyota Celica exhaust smoke

So I just bought a 2000 Toyota Celica with 162,000
miles, and it was throwing a couple codes, so after
a full tune up (NGK Laser Iridium plugs, new coil
packs, engine flush, air filter, oil change) it went
away. This is in good shape, but to be safe I used
Seafoam in the fuel and also the Seafoam intake
cleaner spray, so when I started seeing an exhaust
cloud, I assumed it was cleaning out all the carbon
build up in the engine. The exhaust has a bluish tint
to it, and smells like something is burning, but only
comes out at higher RPMs. When I removed the
coil packs, they all had a bit of oil around one part
of them, halfway down. Some of the codes tripped
were also cylinders 3 and 4 misfiring, which both
had oily spark plugs. It's running fine now for the
most part, but the previous owner said it needed
both O2 sensors and a new MAF, and I put in the
new MAF but not the new sensors yet. I'm thinking
that, while the sensors might not be helping the
situation, that it isn't the problem, I think it may be
the gasket between the valves and the ignition
coils, because if there is a slow leak, that could be
why there is bluish smoke at higher RPMs and why
the last coil packs had oil that started halfway
down, but that's pure guessing. If anyone can help
point me in the right dorection, or if anyone had the
same problem before, I'd love to hear some
feedbacl, and I can use any help I can get.