by -5 boss he means boss o ring fitting. That"s a type of thread like what you would call pipe thread, course or fine thread. The clutch valve body on the left hand side of tractor under battery box has ports. You take the plug out and install a fitting that is boss o ring thread and hook a 300 pound test gauge to the one marked clutch, rev engine up to 1800-2500 rpm and see what you are reading.
Also, if its an early model 4430, on that valve body there will be another plug/port marked lube, this measures your transmission pump pressure, which could also be a problem. Cant remember exactly what it should read but now with my new transmission pump in mine now reads 50 psi, I think it should be between 20-30 psi anyway.
Do you have a service manual? It discusses this pretty well.