I saw this reference to Vaillant while looking into a different question: RV Doctor Question of the Month
-- last topic on the page. Looks like it has been out of vogue for 30 years or so.
Googling on Norcold and Vaillant together produces very few useful hits. Searching Norcold's website
produces zero search results. Mention of parts availability circa 1978 is at an obscure source here
. Vaillant water heaters look to be an orphan product. The only other mention at Forums is this thread
-- member was last online Nov '06 -- she implies installing a replacement Vaillant. Old LP appliances probably need to be checked out thoroughly for safety. You might need to call around to see if anybody has an RV tech who remembers anything about Vaillants.