This is the classic "tranny fix." The transmission is removed from the car, fully disassembled on a bench, cleaned, and inspected. All worn seals, gaskets, clutch packs, and bands are replaced. The "hard parts" (gears, shafts, case) are reused if they are in good condition. A quality rebuild should come with a solid warranty.

What's the best way to sell a used car with transmission issues?

: While "tranny" is common automotive slang for a transmission, it is also a derogatory slur for transgender individuals. In the context of "completing a paper" or submitting documentation, ensuring the use of professional terminology like "transmission" is generally recommended. FIXED RATE | English meaning - Cambridge Dictionary

Pay attention to how the vehicle transitions from Park or Neutral into Drive and Reverse.

An flawless repair. The transmission operates like new.