1) How reliable are the oil coolers over time.  Mine looks to be the
original by the 03/88 stamp on it.

Very! they can be pressure tested.
http://www.benplace.com/oil_cooler.htm

2) Anyone ran into the same type of leak and replaced the oil cooler or hoses

Check the coolant presure:
http://www.benplace.com/pressure_test.htm

A leak may also come from the left head gasket, double check the water pump.

A simple loose clamp could also be the problem, clean the area and watch for
a leak

Ben
http://www.benplace.com/