We had that problem when we picked up our 2004 last year. Turned out to be a cracked mixing chamber (freeze cracked). I found a reasonably priced alternate at Lowe's. You have to look for their "utility" sink faucets. At any rate its almost identical to the original, except it has a cast and milled brass mixing chamber, and not the cheep plastic job they typically put in travel trailers.
1967 17' Hi-Lo Bon Voyage (1967-1969)
1969 19' Hi-Lo Bon Voyage (1969-2011)
2004 27' Hi-Lo TowLite (2010-present)
2015 Chevy Tahoe LTZ