weringhausen, I've got a return filter on the machine as well.Sundance, this rough strainer (150 micron) from wire mesh has a lot of surface and will be okay, not a big chance to clog.
Anyhow if the rubber hoses are in good working order (not falling apart internally) and you don't drop anything in the oil during refill there is not much big stuff that could get in there.
I am talking about a much finer filter and that one should definitely live on the pressure /return side.
Since i fabricated the tank and the rest of the machine I felt it was worth putting a strainer on the suction. Obviously based on the size of the strainer there isn't anything like this on your suction.
Good luck with your issue.