Technical Gelled Diesel - LP pump now sounds like a coffee grinder!

[portland_bill]

Soak the nuts with a proper release agent, like Plus Gas, it'll do a much better job than WD.
As much as possible, clean the exposed threads.
Try to find a small socket and T-bar. That will allow a gentle turn, without any sideways pressure. If they don't easily release, move a little, tighten a bit, repeat, gently working them off a tiny bit at a time.

 

[Matt Quinn]

I'll need to see what's lying around Bill. I'll get as much of the dirt away 'dry' - brush the threads with a bronze brush and vacuum what I can away; then clean a little further with IPA; at that stage I'll apply whatever 'penetrant' I have - and it'll likely get 48 hours to soak in. - My only 'enemy' then is whatever torque was applied in the first place, which I'd imagine wasn't excessive... I do have tiny sockets and a ratchet (1/4") as things this size are common in camera supports (hydraulic pedestals, booms etc). - The ring doesn't look 'rusted'; just manky.

 

[bugsymike]

If the fuel pipe connectors at the pump in tank are the same as the ones on your fuel filter in photo, once cleaned and WD40 they usually release by squeezing both squares on each pipe with thumb and forefinger if you are lucky, no tools required.
You may find an old lorry firm has some "anti waxing" agent, I went to an auction years ago and ended up with several gallons of it when buying another lot, I finally got rid of it and then found too late that one of my neighbours could have used it on his refined chip oil Land Rover.

 

[Matt Quinn]

Thanks Mike.. as it happens the clips came off quite easily with finger pressure. Sadly I'm not quite out of the woods yet (see my other thread, posted earlier today) - but, well, some progress has been made. I've ordered some ant-wax stuff of eBay; should be here in the next day or two. - As will a new filter.