re: P trap help - how would you repair?

The OG plumber that installed this is who fricked you from the jump. Normally in houses the only thing that needs a 2" drain is a washing machine. If I was coming fix this at your house...I'm either

A.) Cutting out that Tee and replacing it with a 2x1-1/2" tee or
B.) Using a socket saver to remove pipe "B" out of the tee, and glueing a 2x1-1/2" bushing into the tee. You can see the bushing glued in to the top of fitting "C" currently

The fitting that is glued above C is called a trap adapter....it adapts from glue style to SJ (slip joint) to allow you to intall a slip joint trap. It has totally missed its purpose by being before the trap.

The trap adapter would be glued into the Tee where pipe "B" is currently, and all connections after that would be made leak free with hand tight + 1/4 turn.

Plumbing is easy to do but tricky to do right. This would be year 1 apprentice work at our shop. Defintiely do not just wrap it as that will not stop the leak and will encourage mold growth in the warm, still and dark of your cabinet space.

That'll be $175