X2 on smacking it with a hammer. I found that the Bosch solenoids are a bit "tight" the way they fir the plunger, sometimes they stick. Also like Que said on the brushes. Usually having to smack it every time means the starter is going and needs a rebuild or replace. You might be able to fix it with a real good cleaning tho, I just took mine all apart and used solvent with rags.
***--- Wrecking Crew member ---***
"I've prolly been around longer than you think"
91 YJ 2.5L 5-spd, 31" BFG ATs, mostly stock NO RUST 172K in WNY, Daily Driver