Where can I purchase a small 12 Volt motor with a "gear reduction" or the like to be used to open & close a plastic heater valve in a car I'm building. I saw one at a car show used to open & close an air vent in an antique car. It opened rather slowly. Was about 4" long and 1 1/2 " wide with some type of transmission or speed reducer on the front of it. I want to be able to push a button and open the valve a second push of the button would close it. Any help would be appreciated.
Jim

How about a 12 volt solenoid valve, or do you need it to open slowly?
Then I would use a latching relay, They are currently used, first one I used were from the old VW beatles in the 70's for the Head light, toggles a single pole/double throw switch(high/low beam)by a momentary contact to ground. Only draws power when switching.

Suggest that you try to find a 12V inline cordless screwdriver. Clamped in place and rewired to run on vehicle current, shouldn't need to do any gear reduction.

If you do the cordless screwdriver, add limits switches so when it is closed, the closed limit opens the close control wire, and the open limit opens power to the open control.

How about something like this:
Hong Kong SAR Gun Type Actuator. Manufacturer, Exporter (http://timberport.manufacturer.globalsources.com/si/6008825426318/pdtl/Power-door/1003649435/Gun-Type-Actuator.htm)
You can increase throw with levers.
The relay described above will allow a momentary press to open, and another momentary press to close,repeat.

Try www.surpluscenter.com

Excellent link from above, here's the page if having problems locating it:
https://www.surpluscenter.com/sort.asp?UID=2009062422083689&catname=electric&keyword=EALD