Is there something that could possibly cause the cooling system on my '91 RS to become over-pressurized? In the past few months I have blown almost every seal, gasket, hose, etc. in my cooling system. What gives?

 

Put a cooling system pressure tester on the radiator and run the motor, and check to see if the system pressurizes quickly.
If it is being pressurized, then I would do a leak down test on the individual cylinders to check for a blown head gasket/ cracked head/block, etc...
If you see bubbles in the radiator while doing the leakdown test, be ready to spend money.

 

Radiator cap is supposed to release the pressure. Put a new cap on.