This is a copy of reply I have sent to several people on this subject. 
Hope it is some help.

Wendy & John
'85 Westy,   "S-CAPE"

What we had to do was take the tank off, sand it all down, remove the ID
> plate so to see that it isn't rotted through underneath.  I guess this is
a
> common problem because there is enough room under the label for dirt and
> moisture to get in and not get out again.  Resecure the ID plate, for
this
> we used an epoxy-steel weld cement, & repaint the tank. The fill valve on
> ours was all coroded.  The valve that was on it originally had a little
> tube coming off of it.  This is for the overflow.  They only fill the
tank
> part way with the liquid propane and  this valve allows for any excess
> overfill to vent out.  This is were the problem lies.  They don't make
this
> valve anymore from what I can find out.  What our propane guy did was to
> put a regular fill valve on it, just like you would have on a 20 gas
grille> bottle.  Then in the upper part of the (when looking at it on its
side)
> tank there is a little square.  As I recall, it was about 5/8th of an
inch
> square.  In this place he put in what he called a "spitter" valve which
> takes the place of the original overflow/excess valve.  Then they
pressure
> tested the bottle and stamped it with the date. We reinstalled it and he
> filled it.  It's perfect!  So, don't give up if it looks like a rusty old
> torpedo from WW II.  (of course, that's exactly what they MAY be).