Old filter head before removal after a new filter with a greased seal had been fitted, and tightened half a turn after contact. Clearly not touching at top right, where it has been spurting from.
Old filter head after removal, new filter screwed on to just touch, clearly showing the warp of the sealing face.
Even the flange that bolts up to the crankcase is warped, unfortunately I didn't notice this until after the new adapter had been fitted using the old sealing ring.
Filter-head hose going through the upper hole in the radiator diaphragm instead of the lower as it should, strap tending to pull it upwards.
This means that the short hose going to the cooler is also bent upwards, although probably not as much as a problem as on the filter head as the strap is tending to pull it down into the correct position.
It was only subsequently I noticed a smooth, bare-metal depression in the inner wing right by the elbow in the return oil hose from the cooler, just visible in the more general photo of the area above. I've never been aware of any knocking, even when the engine rocks quite badly at a very low idle, not even when my head has been under the bonnet. But as the metal is rust and paint free the hose fitting must have been rubbing or hitting there, and that would tend to bend the filter head in the direction it had.
This raises the question of just what angle the filter head should be to the block. In this image it's angled slightly to the left, which puts it very close to the distributor, which it was before. But go too far the other way and the oil hose will foul the alternator. I'm wondering whether it should be at right-angle - at least - to the block, if not angled a bit forwards to give a decent clearance to the distributor. The elbow then being angled away from the alternator to give clearance to both that and the inner wing. There is still a very slight seep from the 'filter head to block' seal, so prior to the next service I am going to have to remove it again and dig the old seal out, come what may. (I never did, and it doesn't seem to be leaking any more).