No...just replace the O rings around the distributor. It's pretty difficult to disassemble the distributor to replace the third O-ring (although i understand it can be done, be careful not to bend the shaft when driving the pin out...the O-ring is unobtainium volvo but there is a Honda O-ring that fits) and most leaks are O-ring associated without the internal O-ring being the cause. Just replace the rotor and cap.

I don't know if there's a Hall sensor in the 90 non turbo 740 engine...check your manual or the FAQ. Check if you have spark at the coil before hooking up to the new distributor.

good luck. Strange there's no codes.....