Missing crush washer.......
 

Glen,

You need a crush washer for that adaptor. Otherwise, you will have oil seeping around it. The epoxy for the pressure switch needs to be just between the metal and plastic part. That’s a little bit more than I would like but you are good. PM me if you need a crush washer and I’ll could put one in the mail.

Tony

Keyla - the Porsche parts catalogs for our cars are all available on line to download as PDFs from Porsche. Free, too. That's the most straight forward way to answer a parts question like this on the crush washer. Catalog shows an 18x22 washer, with a part number (though of course any suitably sized crush washer will work). The catalog with its diagrams is a great resource for a variety of assembly questions as well, even though that isn't its purpose.

It does appear that where threaded fittings under pressure enter the aluminum/magnesium of the case or components, Porsche always used a crush washer, so you were spot on in wondering if something was missing.

You are entering into the realm of personal preference by way of sort of second guessing what Porsche used in the way of nuts. The plain nut works just fine. I suspect most just reuse what was there. It is not subject (in this application) to road salt or whatnot, and is, alas, often nicely protected with a thin film of oil.

The nylocks would be the same as the nylocks often used on the case drain plate, the breather, and other places on the engine where M6 fasteners are used (though the nuts securing the intermediate shaft cover are a different part number, and maybe never have been nylocks?). The catalog gives the same part number for most of these applications, but I can't tell from that whether these are nylocks or not. I like nylocks for the drain plate, they are the norm for the chain housing covers, but I can't say as I ever gave thought to the two nuts holding the generally inoffensive oil thermostat housing in place, or the breather.
Poking around, I suspect that the earliest 911s had plain nuts, and the nylocks are a superseding part. The idea is that in low torque applications the nylon part will resist the loosening effect of vibration and thermal cycles. The early part # is 900 076 010.02. By the '78 catalog, it is 900 076 112.02.

Me, I'd just reuse what was there - it wasn't loose, was it? It is the O ring which keeps the oil where it belongs, not the torque applied to these nuts. I've reused valve cover nylocks over and over again, and never had one get loose just because the nylon part may be a bit worn, hardened, or otherwise less capable of resisting rotation.

Some like to cad plate everything in sight (there is a discussion here about whether to pull all the valve cover studs and have them cad plated). Others just clean the old fasteners and reuse if there are no obvious signs of damage on "ordinary" fasteners (not critical stuff like rod bolts). The engine will perform the same either way.

If you are a shop doing, say, a valve adjustment, it makes sense to order (at customer expense, and with a bit of extra to the shop from their parts discount) a set including gaskets and nuts and washers. No time spent cleaning things. As a DIYer, you may calculate things differently.