I think it was me who mentioned using brake fluid. Works wonders. You CAN also use dirty fluid, like say if you're bleeding your brakes anyway you can go ahead and use the stuff that came out of there.

Afterwards I use WD-40 to clean the rest of it up. I usually soak a bounty in brake fluid and let it sit on the shield for 30 seconds then give it a few firm up and down strokes.

works great.