Replace the O2 sensors, and shop around for them. Bosch sensors are good, and often Rock Auto or Amazon are great for them. They don't need to be tested unless they were brand new, they should all be replaced at this age. Don't cut the cats out, that's a bad path to go down, with multiple new issues. Fix the emissions system.
The balancer $75 sleeve products, that is only for a worn crank seal groove. Those are rarely ever needed, only when idiots don't keep good oil in the engine, and the filth wears a groove in the crank at the front seal surface. Usually any front or rear seal leak, is from the seal becoming old and brittle.
The balancers also hardly need replacing, typically when very old, but it's good insurance to replace them. It's bad when they come apart.
Oil stop leak products rarely work at all. Some may reduce leaking a little, but don't expect much.
Don't use silicone for anything, use only RTV. Silicone is for aquariums and home exterior caulking. Buy only automotive top brand RTV, such as Ultra Black, or grey, copper, red, blue. Those RTV products are very durable, silicone gets hard and brittle with heat or sunlight. I have Ultra Copper and black on my chimney right now, from 150+ years ago. It's tough and barely flexible, but not letting go until you make it let go.
You can add RTV on top of anything which is clean, you can spread more onto other RTV(or silicone, but I'd get any of that tossed in the trash).
