Not stupid... perhaps not wise either.  Pretty common practice on many
British Vehicles though generally single weight non-detergent motor oils are
used.  Remember that gear lube weights are computed quite differently from
motor oil weight so the viscosity isn't as different as the numbers suggest.

That said -- I use Redline synthetic in everything, British or Westy.

Geo

----- Original Message -----
From: "Brenton Tait" <BTait@INVESTEC.CO.ZA>

This might sound a bit stupid...but what are the chances of using a
mineral 20w50 engine oil in my gearbox? DO I run the risk of damaging
it?