I don't know about 617 IP gaskets but all 603 IP gaskets yopu can replace externally are available from MB or Phil. Only the stop lever shaft o-ring is not available and that's an easy one to size-to-fit. Unfortunately the control rod sensor o-ring is a common leaker so a lot of reseal jobs fall short of stemming leaks completely.

Sixto
93 300SD 3.0