Hi,
It's been a while since I played "Tri-Mark Lock" on my rig, so I forgot most of the details. Suffice it to say that the plastic part you have was probably what kept the bolt from extending completely.
You can try to rig something up that will keep it from extending all the way.
BUT....while I can't tell definitively from the pics, it looks like the sliding mechanism might be the style which is made from pot (cast) metal. If that's the case, at this point, I'd highly recommend you replace the entire lock assembly with the new version which has a stronger bolt mechanism. IF that's the pot metal version, it WILL break, it's just a matter of time. And when it does, you're either trapped inside the RV or outside the RV. If you're inside, hope you have a screwdriver handy AND that there isn't a fire. If you're outside, hopefully you have another door into the rig OR you left a large window unlocked and can get in that way. Or call a locksmith.
My original lock broke after about 10 years, and we were VERY careful about NOT slamming the door. It's replacement barely lasted four years. I then replaced that one with the new model and (knock on wood), no problems yet.
Perhaps someone here has some pics to show more details of where the pot metal failures occur. On mine, it's been at those two thin sections of pot metal with the rectangular hole inside. That's the weakest part and it doesn't take much for it to snap.
Good Luck,
~Rick
