I've never looked down inside because I've not had the opportunity to need to. I am usually just replacing a filter so the old one, thats generally leaking fuel, gets dumped in the drain bucket. possibly you could just get a peak at a new one and go from there if you were inclined to replace the O rings-assuming those fuel O rings are available, or replace the filter. if it leaked i would say an O ring is cut or damaged somehow or there was strain on the fuel line so the line didn't want to stay inline with the filter connection. I personally wouldn't take the chance on a previously leaky filter with a possibly replaced O ring. I've been to too many car fires in my carreer to chance that. i know, filters are not cheap, but a possibly leaky filter is a big hazard.
mr48, here is a link from the summit site on the corvette style fuel filter regulator. it is basically a filter installed downstream of the fuel pump and it has a built in pressure regulator set at 58 psi (I think). it has a fuel inlet, outlet and a smaller sized return line.
https://help.summitracing.com/app/an...fuel-system%3F