Whats the best stuff to use when joining oil fixings to sandwich plates, cooler take offs etc. Just the usual plumbing PTFE tape ok?

sandwich plate will come with a large square section o-ring, likewise the filter.

the connector fittings that screw into the plate are sealed via small o-rings or dowty washers.

The pipes have connectors that seal via a concave/convex face when bolted up, much like brake pipes but bigger.

No need for PTFE tape anywhere.

/ wot he sez ! Anything you put on the fittings will probably cause leaks