I have an 80s vintage GDO, with dip-switch programmed remotes, and both of the remotes have died.  Any idea as to what I could do to restore remote door opening?  The GDO drive unit itself works fine, and because of the kludgey way it was installed, I don't really want to replace the drive unit until it dies.  The wired pushbutton controller still works.  It's an old Sears unit.

What I'd like to do is find some kind of RF gizmo with a momentary-on output I could parallel into the wired control input.

tia.

look for an old one on ebay

Just bite the bullet and replace it. You know you are going to have to and it will be cheaper now than down the road.

Still have the remotes?

What is wrong with them?.... Is it possible to clean them up and put them back in service?

Did both remotes stop working at the same time, or one before the other?  If both stopped working at the same time I would be suspicious the problem is on the opener end.

Get an arduino, and wire it to control a relay to control the garage door opener. Then use your phone to open it.

Or bluetooth in a couple ways:

Overhead door locator

See if they have a location near you, had to replace the openers for the big bosses house and the had them in stock.  Not cheap for what they are but much cheaper than a new unit with installation.