a sharp tap with a hammer works for sticking starter motor solenoids too 
I preffer no bounce when its not covered/painted.
Top of my head:
-old honda, throttle cable started getting sticky in one, so one day after school I tried starting *bu, bu, buu, vroooooOOOOOOOOOOOOOOOOOOOMMM
MMMMMMMMMMMMMMMMMMMMMMMMMMMOM
GWTF!* Shut her off, poke around, couple taps behind the throttle, *tink*, some WD40, and straight to the shop for a repalcement it went (if it wasn't a manual or as old as I was at the time, probabley would of towed it).
-bonco II spare tires
-old honda thermostats (alternatively, old honda electric-driven radiator fans)
-mercury outboards (well, half the time it's legit, the other half are purely rage-filled.)
-trailer hitch, post-uncle/relative (the last episode called for 20lb Bertha)
You guys metnioning gas tanks and motors - I'm thinking the next thing that I'll be giving the treatment to is that retarded evap sensor on my CRV's gas tank that lightsup everytime I torque my gas cap to 24 rather than the required 25 (seriously).