Cats and Oil

[Michael Bradley <mbrad@microsoft.com>]

I have a 94 90 Q with about 34 K miles. In August I replaced my LHS cat as
it
fragnmented and clogged up the works. Last week  the RHS  went. When I asked
the dealer what was the cause he said it was an oil problem. The dealer has
used
Castrol GTX (as I have for years). Apparently it contains  a zinc compound
that
is hard on certain cats. He has switched to Castrol RX. Apparently Castrol
is not
unique here as any number of other SE grade brands also contain the
same compound.  I have used Castrol GTX for yearts in other cars and never 
experienced a problem.

Anybody with similar information?