David,
We had the same problem when we bought our 85 Westy. This is a federal,
DOT,
Department of Transportation thing, not a state regulation.  The tanks must
be recertified every 10 or 12 years, I think 12.

To be on the safe side, I would have the propane company get rid of any gas
that's in the tank, they can evacuate it safely.  They should see the tank
in place so they are sure of what you are doing.  This is the instructions
we got from our propane dealer.

Remove the tank from the van, wrap your spuds, the little brass connector
things in cloth to protect them from dirt and grit while they are undone.
Don't quote me on this but as I recall the threads on this are backwards as
on all propane stuff, check with your propane dealer first.

Sand the tank, removing as much rust as possible, and take off the small
metal "tag" that identifies the tank.  Clean this tag up carefully as you
must be able to read it when you are done so don't go hog-wild with the
sand paper. As I recall, this is about 3" square.  KEEP THIS TAG.  The
reason they want you to remove this tag is because dirt and moisture gets
trapped behind it and it is usually the first place to rust through or
become so thin that the tank  won't hold the pressure.  We removed it by
using a Dremell cutting wheel at the tack welds in each corner of the tag.
Sand the area under the tag.  Take it to a place the services, supplies and
repairs home propane tanks, not just a "fill station", bring the metal tag
with you.  They will pressure test it and stamp it (somewhere on the tank
itself) with a DOT stamp and date if it passes OK, which it probably will.
Then take it home, resecure the metal tag, we used a "metal epoxy" which
was a two part epoxy that hardens like steel,  prime and paint with any
good metal paint.  As far as the valves go, that a piece of cake for the
gas co, they can fix it for less than $40.00, the original valve may not be
available but they can install a "spitter" valve which is essentially an
overflow valve.  The tank only get filled about 2/3rds of the way, leaving
head space for air so the liquid propane can be turned into a gas.

After re-installing the tank, do the soap test on all the fittings to make
sure they aren't leaking or have the propane dealership do it for you, or
as a last resort, a VW shop.

Good luck, happy camping. If I can be of any more help let me know

Wendy & John
Cape Cod, MA

'85 Westy,   "S-CAPE"