I replaced my O-ring.  took off my oil filter and decided that I needed to
buy a 27mm socket to get that nut off.  Came back from flaps and found that
I didn't actually need any socket, because the nut was actually
loose!  Maybe I could have just tightened it and fixed the problem, but
since I was this far, decided to replace it anyway.  Others may find that
the nut just needs tightening.  I next went about trying to remove the pipe
that goes up through the oil cooler.  I didn't have another nut to use as a
lock nut, so I cut the top off of an oil filter, and used that.  That pipe
was pretty tight, but it came out.  Then there was actually plenty of slack
in the hoses to move the oil cooler, pull out the old O-ring, and put the
new one on.  Put it all back together and torqued the nut to 18
ft/lb.  Haven't tested it yet because I realized I don't have oil to put
back into the crankcase--D'oh!
Edward