My '76 has black undercoating that looks very professionally done, as if it came from the factory. On a German 914 board I am told no 914s ever came with undercoating from the factory. Who's right?

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Sorry, cannot speak to the Euro market. In the central-to-east US market, most 914's were cajoled into being rustproofed by the dealer. New 914's came un-rustproofed by the factory, but most customers in thos areas either gleefully had it done, or were coerced into it. In every US market, with the exception of the west coast, it was probably a plus "at the time". Through the 30+ years of these car, any have seen that rustproofing dry & split, allowing moisture to trap itself underneath. And, we all know what that leads to.

My '72 was "proofed". For 10 years it was a sticky as flypaper. Then, I noticed it wasn't sticky anymore & worried about splitting. As part of my regular regimen, I wipe down the entire areas coated with WD40. Makes it flexible again & almost sticky.

In the long run, I believe it was a good decision, since I drove my car to work everyday on salty roads for about 4 years.

Will I do it again on my next 914? No. Served its purpose on a garage queen, though. When/if the garage queen needs to be re-done, I'll remove it. Hasn't seen rain/snow/mud in over 25 years - doesn't need it & I'd rather have bahia red on the bottom. But that's just MHO.

OK, that makes sense then.

Since I'm stuck with it and attempting to remove it will cost too much time and effort (and since the sheetmetal is 100% clean without any indication of rust anywhere) I will end up putting a waxy transparent material over it to close off any cracks. I'll see how that works.

PVC undercoating was a factory M-option, M640.
This was applied before the paint, so you have to look for the orangepeel surface to know the paint is not is not on steel. Using a magnet, the attraction is weaker on the undercoated steel than on painted steel. Say, the inside and outside of a fender. Most Canadian cars have the PVC, and the heated rear window. The PVC is white and up to about 1/8" thick in some areas. It adds a fair bit of weight to the body.

BTW, since your undercoating is black, and hides the paint you can be sure is was applied by the dealer. Further, the undercoating is on the suspension, another clear sign it was not factory applied.

This implies mine is definitely not M640 since it was put on top of the paint.

and it's not at all that uncommon to have both, the gray-ish factory stuff under the paint and the black stuff on top of the paint ...

both are a pain in the butt to get off ...
Andy

I won't try to scrape it off, I feel I'd do more damage than help with the current sheetmetal condition. I'm going to see if sealing wax as used for body cavities can act as a cover on top to prevent water seeping into cracks.

Yes as below quoted in other posts........IT Was Not factory...
Actually if you are an Absolute Concour Purist..
There should not be a 'Spec' of it on a 914...
ALL of the 'Colorado' cars I have sent to 914 Heaven......
NONE of them had undercoating..
Which is strange..seems this would be the place for it!!!
NOW to Address the removal of it...
Way too much time..And will take some paint with it.....
And it gets everywhere.....

Well, I'm a purist, but I don't get into the concours side of things, I just want the car as original as possible for my own enjoyment.

I fully agree with removal taking too much time and most likely damaging the paint as well. I'm not removing any. I have decided to spray the same type of wax that is used to treat body cavities over it. Even though this isn't a "fire and forget" solution and will need periodic re-application in some places it is transparent and the wax is specially formulated to creep into cracks and underneath moisture.

I have spoken to some old-time mechanics here in Germany and they claim some people would take used motor oil, spray the underbody with that, and then spend some time driving down sandy/dusty roads so they end up with oil-soaked sand and dust underneath the car...