Thanks ctaylor, that would explain it, dammit.

I guess a sticking piston has caused the rotor to warp, looks like a trip to the junkyard for some bits and pieces.

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306D 1975 (camper) - rusting away
W116 450 SEL 1975 - sold
W114 long wheelbase ambulance, 3 litre diesel 1974

VW Golf 1 convertable - midlife crisis item
VW T4 van - support vehicle