Soak it with penetrating oil (many listees have said that "Kroil" works 
real well).  Without damaging the bolt head, give it a hard tap with a 
hammer (I use the round head of a ballpeen hammer).  This sometimes 
breaks the corrosion bond.  Try again.  Soak and repeat several times, if 
still no, try a piece of pipe or breaker bar.  Be careful, you might 
crank the head right off the bolt.  I would soak it for a few days before 
giving up.
Good luck,

Charles
'83.5 Westy
'69 280 SE (back from the grave)

On Sun, 6 Jul 1997 RubatoGuy@aol.com wrote:

> In checking out my '88 Westy, I decided to take a look at the spare,
> Unfortunately the 19mm bolt that hold the tray that the spare rests on does
> not want to come off. Any clever ideas? I was thinking of just finding a
> garage with an air wrench that I could talk a mechanic to applying to the
> bolt.
>