My Spit 1500 ones were working perfectly well, until I never used them for 2 years. Same problem won't unlock.
Last week I took the door cards off and spayed 3 in 1 oil everywhere. Wiggled the catch inside a couple of dozen times and then keeps using the key.
I did this wulith the door open and used a screwdriver to latch the lock to simulate closing the door. Now works a treat.
Danny