In the process of doing up the D2 I have stripped down the hydrualics Tank/pump (No. 41 front mount & running a No.2 toolbar blade).
When I opened up the Hydrualic tank it appears that a previous owner has fitted a home made filter on the retun side. Basically they have plated off the baffle and directed the oil flow through a paper medium filter. There are gaps - so it does not take the flow of all oil (eg: If filter blocked up, the oil would still be able to flow into the tank).
I like the idea of a filter in the hydrualic system but do not want to run a non-standard arrangement, so thought I would put it out there to you gents and ask your advise.