I've seen 'em simply be stuck, and a short bit of "agitation" by moving it and it springs up.
Sitting is the DEVIL for these worn out old whores.
Achieving some sort of normal pressure is half the battle, bent leveller arm, seized valve, ancient lube inside finally gone hard enough to block movement...
The only reason they go, is if they keep going. Park it on dirt for months at a time.... trouble.
It ain't yer Dad's Oldsmobile...
Happy coaching!
Buswarrior