Let's see... the door button has this small rod attached to it (maybe 1/8" dia)... the old one was a solid piece the new ones are two pieces sandwiched together. On my 56, the driver's door lock was original (with no outside lock). The passenger side had been replaced. I didn't find the little rod on either door worn that much that it wouldn't push on the tab to release the lock. It'd have to be pretty worn to shave off that much.
BUT what I did find on the passenger side (the door that was giving me trouble not opening fronm the outside) was that the little tab that the little rod pushes against was getting hung up.
I think there are two solutions to the problem...
1) Buy a new inside mechanism
2) Cut off the little tab like I did. The only big downside is that I can't lock the door from the inside now. Need the key on the outside. But at least I can now open and lock her up.
By the way, Option #1.. I think you still end up with a double-lock problem as I described above in prev. post
