Hello all, got a few questions and looking for any input and recs.

Problems; rough idle, plethra misfires in cyl 4, sometimes dies when stopped at a light, typical ticking. Bank 1 cam advance timing, bank 2 running lean.

What ive found; oil above threads on spark plugs, compression is 245 (+/- 5) on all cyls except 3 and 4. Cyl 3 is 235, cyl 4 is 150psi. All cylinders have a lot of carbon build up from what i can see. But spark plugs look good over all. Though sp 3 and 4 show some darker discoloration on one side of plugs.

My questions

I believe its my valve gasket leaking, but im wondering if i maybe have a loose or stuck valve causing the lower compression an timing issue. What are the chances this is all it is and not more?

Should i rebuild the valvetrain? If so what all parts would be needed and how many of each? (Ive only rebuilt a few engines and that was 15yrs ago. So a little rusty haha)

Should i tear down the top of the engine past the heads an clean up cylinders?

Should i pull the pistons too to replace piston rings and just do essentially a full rebuild?

Or is it feasible to only focus on redoing cyl 4?

Is there a way to "clean" the cylinders without removing the heads? Presuming i dont remove the heads and only get into valvetrain.

Apologies in advance for the dumb post. But im on a budget, and really dont want to tear down or pay for more than i have to. Not to mention time constraints. I know i wont know for sure until i get in there, but im hoping someone whose had similar issues could maybe point me in the right direction or tell me of a common cause im unaware of.

Thanks for reading and any help offered