I am almost ready to remove the cooler after my big oil leak. Have new
O-ring, new filter and oil ready to go, and an exquisite 3/8 internal
pipe wrench.

Question:: Does the big nut threaded on the pipe though the oil cooler
have to come off before the pipe itself can be backed out? Or is the nut
there just to set the position of the cooler on the pipe?

I ask for two reasons:

1) 24 MM is the largest socket I have - I don't what size that nut is -
and if I have to buy one - I would appreciate someone telling me what
the correct size is.

2) The nut on the pipe has shoulders - and I don't think it will be
possible to get a socket to fit to it and hold. The nut shoulder extend
above the surface of the recess it fits in, but with the shoulders
rounded  - factory rounded it's obvious - the socket won;t grip.

Will just reefing on the pipe with the internal pipe wrench - without
loosening that nut - do any significant damage?

Any ideas as to how to approach this little project?

Thanks,

John