JimP mentioned on the Sling Builders forum on Facebook about using a different regulator for the 914 than the default one supplied with the kit.  Seems the default one has had a history of failures and there are better regulators out there.

Van's uses the German made Silent Hektik F4120 and looking at the web page for it I'm also convinced that it is a much better choice.  Also notable is they say that any regulator (not just theirs) should be in the engine compartment and not the cabin as it needs air flow to keep cool - otherwise you're asking for premature failures...  So, I'll have to move that mounting to the engine-side of the firewall.