So this morning I noticed a faint hissing coming from my engine bay. Turns out to be coming from the hpfp. Can anyone tell me what these circular 'plugs' are and can they be serviced i.e. replace orings, tightened, etc...

 

...also, the pump seems to be working fine, apart from the slight leaking coming from the top of that second plug. No stalling or hesitation at all.