I just got 2 Filtermags GP101 for my differentials in my truck, if you don't know about them, they're magnets about 1"x2"x 3/16" that have a 20lb pull. You put them inside the gear box and they collect all the metallic particles. I'm going to get one for my oil filter on my truck also and thought y'all might be interested.
http://www.filtermag.com/wp/products/spin-on/

https://www.expeditionexchange.com/filtermag/

http://www.summitracing.com/parts/ftm-gp101/overview/

I use them on every thing I own with a spin-on oil filter... Which is basically everything except my old 4 wheeler. You'd be surprised what additional crap you get out of the lube oil. On my trans pans and differentials I have gone to the hardware store and gotten the bolt pickup magnets and stuck them on the outside. They easily grab crap thru the cover or pan.

That pretty cool. The drain plugs on my fords are magnetic> Had one come aprt years ago and the plug was loaded. on my 7.3 they are always clean. Are they just not enough, do I need more?