If the Service Vehicle Soon warning appears, and you don't have access to a scan tool, there is a simple way of determining whether the oil pressure sender is at fault.
Unplug the wiring connection from the sender. If it's full of oil, the chances are good that the sender will be the culprit behind the service message. If the connector is dry, the fault could still be the sender, but leaking oil senders is such a common fault with early Alloytecs that it's worth checking for the oil leak anyway.
There is a seal within the sender that is designed to keep the sensor mechanism clean and dry. The seal fails pretty early on, the oil gets into the guts of the switch and it faults out. The oil, which is under pressure and very hot, is then able to exit into the connector. There is a seal around the connector so the oil is mostly trapped within the connection and quite a bit will escape when you unplug the wiring. Unfortunately, cleaning out the connection doesn't fix the problem but if oil is present, the switch is stuffed anyway and is very likely to be the cause of your SVS message.