More than 50 years ago, Mr. Transmission's technicians performed their first fix-up job. In the half century since then, the staffers have become experts at repairing manuals, automatics, and semiautomatics. They offer maintenance for transmissions and can rebuild them more effectively than a squirrel can stash things, be they acorns or auto parts. Mr. Transmission also offers free performance checks, a nationwide warranty, and AC tune-ups.