Found the relays on ebay but then I drew out the rest of the circuit.

I've never dissected a commercial guard controller before, curious stuff.

There are 4 switches tripped when you close the guard, they pair up and close 2 relays. When both relays are shut the guard is accepted as shut.

A third relay closes when you open the guard, this relay has to stay closed for normal operation.

As the other two relays close they cut the third relay back to a holding current. If any guard switch opens momentarily relay number 3 lets go. If the switch should close again the holding current isn't enough to reset it.

Basically, lose any guard switch and you have to open and close the guard before you can restart the machine.

The circuit is dependant on the holding current so changing relays seemed like a bad idea. I had to clean the contacts.

If it plays up again I will rework it and drag it in to the 21st century.

While tracing the circuit I noticed one of the solenoids on the hydraulic valves had had it's connection broken off, probably in transit. Bummer. Luckily the wires are still visible so I should be able to patch it.