I bought a house (built in 1992) with a garage door opener, but no manual and no remote. My opener model is a Craftsman 139.53615sr. I see many remotes for sale on-line, but want to make sure I buy the correct one for my opener.

I can't determine the correct remote from the Craftsman web-site -- but may be looking in the wrong areas

Does anyone know which part I should buy, or where I can learn the answer?