Being an extreme fan of Red Line Oil's products I would use their 5w-30
in your cold climate application.  Trannies need all the lubrication
they can get, and a pure synthetic turbine oil base stock product like
Red Line's will provide the most!  http://redlineoil.com
--
Stuart MacMillan
Seattle

'84 Vanagon Westfalia w/2.1
'65 MGB (Daily driver since 1969)
'74 MGB GT (Restoring sloooowly)

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

Stripped and gone but their parts live on:
'68 MGB, '73 MGB, '67 MGB GT