Where to fit a magnetic filter to a system

[boolie]

You're one of the lucky ones, unfortunately those filters do have a habit to leak, that could be down to people playing with them of course.
I've probably seen more that have leak marks on them than ones that don't.

I think you've hit the nail on the head.. leaks are probably due to people tampering

However, I must concede that the manufacturer's instructions from fernox are not clear. They should make it clear that there is no need to remove the lid and that the seals must be replaced if you take the lid off +you have to be very precise as to how much you tighten the lid