I've had the pleasure of working extensively on only about 4 914's.(either restoring or parts cars) I've had parts sent to me (mostly form SoCal) from at least 8 other 914's.
The '73 that I am restoring now has been under coated with what appears to be seam sealer up to 1/4" thick in most places. The entire underside, wheel wells and inside fenders is coated with a white, still soft and flexible, under coating that when removed seems like the same material as the seem sealer is used on this car. Where ever the under coating is damaged or scraped off there is alot of rust. Where ever it is in tact, the steel underneath is virgin.
Of all the other cars or car parts I have worked on or parts received I have not yet come across that substance until now.
Is it common?
Is it just for northern cars?
Was it a factory option? It appears to have been put on at the factory before anything was bolted onto the chassis because nothing else has it on it.
Just curious.

what areas is it removed on?

the donuts?
or are there areas that have been removed by something like rock chips?

strange.
or all the 914's ive looked at ive never noticed anything like that and i kow mine dosent have that.

-jim

Areas that where damaged by a jack or bottoming out the car or heat from the exhaust things like that is where the coating has rust under it. The floors and frames where completely rotten but it appeared all that rust came from the inside out.