Series 3 Fuel injection pump - leaking from housing?

Afternoon all,

Noticed a diesel leak when I recently parked up, dribbling down the side of the block, clearly from the injection pump.

Bit of a clean up and it's coming from the side that faces the bulkhead, a dribble rather than a squirt.

Removed the injection pipe to cylinder 4, then removed the union from the pump body. New copper washer and fuel line back on but it's still leaking, despite more fettling.

Any idea what else could be causing this? I'm looking to replace the unions just in case, but I've wondered whether the pump could be leaking from the body itself, where the body size changes small to big?

I can't actually see it coming from the union or fuel line, but its definitely from that area. It then flows around the casing anti-clockwise until it drips down the side of the pump.

From watching a couple of videos it looks like it's maybe leaking from between the pump head and main body.

Can this be fixed in situ?

The o ring this chap is pointing to is looking most likely, I can't see it being from that union to cylinder 4.

I've ordered a rebuild kit for my pump, DPA 3249F750 from injectionpumps.co.uk for around £50.

That includes the rebuild kit, gaskets, seals etc, two vanes and the pump liner.

Handy interactive parts diagram here...
https://injectionpumps.co.uk/interactive/interactive-cav-dpa-parts-diagram.htm

Fortunately I've got a spare pump I'd planned to rebuild later down the line, so I'll just use that one to save taking mine out just yet.