After noon , you need to buy the TWO O rings seals that filter between the filter hounsing & the engine blck . Due to age , time & anything else we can blame the seal become flattened & that is why the leak has occurred . One is a simple O-ring , the other is a linked 3 ring seal . Clean the grooves gently , remove any corrosion on mating faces & use a dab of grease to secure the seals prior to installation .
https://www.skandix.de/en/spare-part...using/1028059/ is your most likely failure
Good luck hope that helps you sort your problem
Steve