10w/40 is fine for a new or low mileage engine, but as the 2.1 ages you
need a higher weight oil, I use 20w/50.  I have an oil pressure gauge,
and I can see the pressure drop in direct proportion to the time driven
in hot weather, and it is especially dramatic when climbing.  The main
bearing saddles open up a bit and the oil thins with heat, and the
higher the mileage the worse the problem will be.

Bring your own oil if they don't have 20w/50.

--
Stuart MacMillan
Seattle

'84 Vanagon Westfalia (converted to 2.1)
'65 MGB (Driven since 1969)
'74 MGB GT (Restoring)

Assisting on Restoration:
'72 MGB GT (Daughter's)
'64 MGB (Son's)

Parts cars:
'68 & '73 MGB, '67 MGB GT