door lock won't open

The Trimark door lock failed on our Class C.....could not open door. Ultimately found out that Trimark T-507 lock assemblies had a defect.....the latch bolt was made out of pot metal.....many broke over the years. The new ones now are made of steel.

Ours is a Trimark and the deadbolt key no longer works in the lock. Fortunately, we were able to finally unlock it and get in but we no longer use it. Just the door latch lock. These Trimark door handle/locks are junk and fail often leaving owners locked out of the rig. We are looking for alternatives to Trimark. This is our third lock that has failed. The deadbolt works using the inside locking lever so the problem is the cylinder which can't be replaced. Chuck

We bought a new,class C, Itasca in 2017 and that winter the door latch broke. Got a new one under warranty, It also broke. Went to a small place that sold RV parts, and got a new one but different make, and it's still working fine.

Ack, no! Oil in a lock cylinder works temporarily but is a long term kiss of death. It attracts and traps dust which kills the lock in short order.

Locks should only ever be lubed with dry graphite. They make tiny lifetime supply tubes of it for the express purpose of lubing locks. They cost $2 or so, are mostly air, and use the air to blow a small amount of graphite dust into the lock. Flick the tube a few times with your finger, blow a couple squeezes into the key slot, insert key and work it around. It should free up easily.

Do be aware that RV door locks of that vintage and style suffered a manufacturing flaw, or at least some of them did. The defective ones were supposed to have the key inserted and withdrawn ONLY with the blade vertical, but the defective ones could have the key withdrawn with the blade horizontal, and when that was done, it could freeze up the lock permanently. Those had to be drilled out when frozen. Hopefully yours isn’t one of the defectives and the graphite lube does the trick.

As mentioned above try lubing it, squirt oil in the key slot. Use a light oil, even penetrating oil.

In addition to that try running the key in and out multiple times. It's possible that it could be gummed up in there and one of the pins is sticking.

Also, after oiling it, try tapping on the key cylinder with a small hammer or similar. This may dislodge a stuck pin if that's the problem.
Tap tap,tap, insert key multiple times tap tap tap, key in and out again.
Then try turning it. One stuck cylinder pin will prevent it from turning.

Fortunately, these door handles and lock systems are widely universal. Should be no problem finding a replacement if needed. Yours will likely fit my TT and the neighbors MH and everyone elses too.

Before you drill it out try lubricating the lock cylinder.

You can drill out the cylinder then turn the throw on both the deadbolt and lockset. It takes a while to drill them out, and cheap bits will wear out before you complete it. The only way to tell if something is stuck in the key alley is to disassemble it.