Oil leak behind Air Pump Pulley

This (the seal OD slipping out of its bore) is a known problem. Many Mechanics intentionally take a centerpunch and put several deep dimples into the bore surfaces (at about the midplane of the seal OD surface) on both the engine block and camcover in order to "hold" onto the seal better -- next time you have the 1-4 camcover off, add 6-8 equally spaced dimples around the circumference of the bore.

 

The distributor seal has to be pressed in (into a single solid piece) so the "dimple" technique isn't so appropriate (i.e., the protuding rim of the dimples, if you can add them , would score a trench in the seal OD sealing material during installation, and none would be present to expand into the dimple) -- for this one, it's better IMO to machine a shallow groove in the bore (i.e., no material protruding upward from the surface, but a groove that the sealing material on the OD of the seal can expand into -- like on the cam seal bores) at the seal OD midplane. If you do have trouble here, it's less of a hassle to fix so probably fewer cars have any modification done here.