Hi, you'll understand from the attached picture just try to push the plate back as to not disturb the non leaking pipes release the bracket which holds them to the chassis as to be able to pull out the leaking pipe and replace the seal, this one:
https://www.lrdirect.com/RVW100010-supplied-by-LRDIRECT-branded-OEM.html but order 4 x
https://www.lrdirect.com/ANR6700-supplied-by-britpart-branded-oem.html and change them all . After you pull out the pipe do somehow to clean well the hole where the seal goes and put oil on the orings. that black thing on the seal is just to hit it with a hammer untill the seal is in then disposable.
For the future you can remove the block or buy a used one and addapt compression fittings to it for flexible pipes see this
ACE fluid weep front of valve block ... you can prepare all you need to be ready to fit then at a point you can convert to flexibe pipes and you'll be leak free for eternity, the market is full with cheap(ish) valve blocks due to the de-ACE hysteria of those who choosed to get rid of the whole system due to a leaking pipe or some other fault, e.g
https://www.ebay.co.uk/itm/Land-Rover-Discovery-2-Ace-Valve-Block-Pump-In-Good-Working-Order/223972288014?_trkparms=aid=1110001&algo=SPLICE.SIM&ao=1&asc=225114&meid=55f6c72e6a6542e48d27175415ac7d76&pid=100010&rk=2&rkt=12&sd=324114485503&itm=223972288014&pmt=0&noa=1&pg=2047675&_trksid=p2047675.c100010.m2109
i have the whole setup(modified block + pipes) prepared but not fitted it yet, i'll wait for a leak first, costed me the equivalent of around 150 quid all in.
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