αlexander

I had that too. It's a relatively straight forward fix if you've got the right tools, see any Toyota or Lexus service manual for step by step instructions (it's not like they change how bearings are mounted very often). If you don't have the required puller and bearing press, take it to a shop rather than hammering stuff out and risking additional damage/ruining the new bearing. Any reputable shop can give you a quote for this over the phone.

Have you tried inspecting / replacing the ignition coils? Could be a crack in one of them that's causing spark to ground out before it gets to your wires. Other fun diagnostics - check for proper compression on all cylinders (0 compression on any cylinder would cause symptoms that are far worse than you've described, but marginal compression will certainly contribute to a misfire), examine the exhaust for steam or monitor coolant levels closely to make sure your engine isn't sucking coolant through a blown gasket (water in the cylinder... uh, yeah that'd be bad). I wouldn't worry about the plug seals leaking. Water may get down to the top of the plug, but the threads holding the plug to the engine will do a good job of keeping it out of the cylinders.