A second reason for the magnet.
A few years ago, a Stromtrooper in Massachusetts ran over some metal which
popped up and pierced his oil filter. This event immediately produced two
problems, shortage of oil in the engine and unwanted lubrication of the rear tire.
He made it home safely, noticed the puddle, rectified the problem, and
soon bought an accessory to protect the vulnerable stuff near the filter.
Ironically, this reduces his ground clearance so the plate gets scuffed
on a ramp at a place where the Stromtrooper frequently must go.
I am a cheapskate. I salvaged a magnet from within a dead hard disk drive,
stuck that on the front of my oil filter, and stuck a tin can over the filter.
The magnet keeps my can aboard, and my oil filter is, at least marginally,
protected against "bionic road kill". In fact, I found a second tin can that
fits over the first one well enough, so my filter is doubly armored.
Perhaps this has been a waste of time, but it provides cheap confidence.
Keith