1996 licoln towncar gear selector

No not the whole transmission. Could be a band or servo. It still has to come out and be tore down to fix.

Does you shift indicator point to "R" when in reverse. The reverse light are switched on by the selector shaft position sensor built into the Parp/Neutral Safety Switch. It may be bad or just out of adjustment.

It sounds like a gear shift alignment switch/linkage...Try your mechanic before a transmission shop. Should be less costly, and only address the alignment of the selector.

sounds like the cable from the gear stick to the gearbox selector switch has been put on wrong ,put the car into reverse so that the reverse light is on , turn the ignition off and find the gear selector on the gearbox , pop the end of the cable off it then put the gearstick into the "R" position and refit the end of the cable back onto the selector switch , hope this helps

Put the vehicle in Park, disconnect the shifter from the shift lever on the trans, adjust the linkage or cable so the connection is clearly a slip in/on connection and tighten things back up. Hopefully this will solve your non-reverse. As for all the gunk and metal shavings, friend, you better have another tranny standing by in your garage when this one stops working completely.

Could be as simple as low transmission fluid, but it can also be your shift solenoids or gonked up valve body. Star with checking your transmission fluid level. On that vehicle its pretty simple. There should be a yellow dipstick. Vehicle needs to be on and on operating temperature. Gear selector in P or N. Pull the dipstick out and see what it reads.

I assume the car is automatic transmission ? Can you select a lower gear manually using the selector ? Also with the engine running, parking brake firmly applied and the car in Drive, check the automatic transmission fluid is at the correct level. The dipstick is not present on some models however, which is a pain, and would require a dealer visit. If the stick IS present, its on the left side rear when viewed from the front of the car, make sure the fluid is between the two marks.
If your cars is manual/stick shift and it drives in reverse normally, but not in any forward gears then you have a selector issue or internal gearbox failure.

If Drive Selector switch is properly aligned then a shift silonoid might be the problem.

what kind of vehicle is it?

You need a new inhibitor switch on the gear selector.