David Beierl set me straight on this and with his permission I'm passing this
on to the list.
My propane regulator developed a leak shortly after I bought it in CA. I went
to a RV supply store that also sold propane and brought my old square type
regulator with me. The salesman I talked to showed me a round type
replacement for about $8. It looked like a standard BBQ type regulator that I
had recently picked up at a swap meet for $1 so I thought great and just
installed it. Since then we moved to NM and I recently started to work on the
fridge because it wouldn't stay lit and I thought it was an air leak or
regulator adjustment because of the altitude change. I had seen the list
recommend to other people with leaking regulators to just go to KMart or
WalMart and pick up a replacement for about $8 and since this is what the
(obviously new) guy at the RV store told me I didn't think anything about it
and passed on the same mis information. The following is the straight story
from David:

Marshall Brass 290 is the replacement for the no-longer-made Marshall Brass
260 (square) regulator.  It looks like a small circle stuck to a big one,
and it's a couple inches longer than the 260, so you have to bend the
tubing going up into the van somewhat.  Costs about $25 with installed POL
fitting, plus a few bucks for the weather covers.

              ...and when I asked him what the difference was:

1) Illegal as hell
2) Doesn't have "excess-flow" POL fitting that shuts off propane if a big
leak happens.
3) Doesn't regulate closely enough to run the fridge properly
4) Wickedly illegal
5) BOOM if you have an accident (see number 2)
6) Not approved for RV use (see 1, 2, 5)

 You WILL NOT find the correct regulator at KMart, WalMart, or your local
hardware store most likely.
Hope this helps,

Ken Hunter
82 Westy 1.9D
84 Jetta 1.5D
89 Mitsubishi van