If it is a Bargman L300 then here is the info I got while researching a replacement... the info below is comments from multiple sources.
I've included a photo below of the inside of my door (the blue strip is the tarp that was over the MH when the photo was taken).
Note that the failure mode is that you get locked out. I was lucky, I had left a window unlocked and with a handy stepladder was able to pop out a screen, slide the window open and climb in.
- - -
The Bargman L300 was used extensively from the late 1970's through early 2000's.
The L300 cutout is 4 1/2” x 5 1/4”
Trimark # 33677-01-K (was 31158-01-K until they renumbered the products) will replace it.
The Bauer 20-2084 is marketed as a direct replacement. See https: //
www.rvshop.com/Bargman-L300-Replacement-Lock-by-Bauer-_p_73883.html
The Bauer BP-12 is frequently is a better deal (price-wise). Bauer is at 866-682-2837.
http: //
www.bauerproducts.com/product/bp-12-with-pin
The "with pin" is important - if your coach has two alignment pins protruding from the door and aligning with slots in the frame.
Another resource: "jack@pacificrvparts.com" is very helpful...
https: //
www.pacificrvmirrors.com/category-s/4160.htm
And the AP 013-257 supposedly has the same dimensions and will work. Don't know if it's a direct interchange or if it is a quality unit or if it is cheap junk.
- - -
I ended up removing and disassembling my L300, cleaning it, and the local RV shop gave me one that had been removed from a mid 1990s customer RV... I was able to make a frankenstein using parts from both and am still using it. (frankenstein: something assembled from spare parts)
But I intend to replace mine eventually.
I'll be watching this thread...
Mike