Working out a head gasket failure

[Andy Bennett]

Finally had the opportunity to have a free couple of hours to tinker.
Timing all sorted after a few runs and minor adjustments and all running nicely now. Had a couple of runs out and head seems to have settled.
But...
I have had an oil leak from the rear of the engine for a while now. I had previously had a loose nut between block and crankcase which had resulted in similar,  I also wondered if it was the valve cover seal.
As I had added water to the area from removing the head I thought I would take the valve cover off to check and reseal etc and investigate the oil leak. Long story short, the nut was tight and I resealed the cover. In then cleaning everything up and running the engine the source of the oil became clear:
   

I haven't had to replace an oil pump before but if my understanding is correct this is just a 'loose' cover with gasket underneath and which is held in place by the block?
If so, other than removing the block to gain access to renew the seal it seems I have little choice but to add something like RTV silicon in the hope that it covers and seals?
Andy