[GGA]

The T handle on the garage door is quite old and the key won't open the lock. There is no other access into the garage. How can I open the door without damaging it?

 

[DexterII]

The first thing that I would try is some Lock Ease, which you should be able to get at your local hardware, auto parts store, or big box. Carefully work it in and out of the lock with the key.

 

[Ron6519]

If lubrication doesn't work, try PB Blaster or liquid wrench. Let it set for a few hours before you try to turn the key.
If all else fails, pick up a new lock and cut this one off.
All exterior locks should be lubricated at least twice a year.
Ron

 

[fabrk8r]

Do you have access to the garage through a walk-through door? If so you may be able to lubricate and free the lock easier from the back side.