Can be changed easy enough.
Most dodgy solenoids are BOSCH, come across them all the time starter fine solenoid crap and jamming, worse when hot.
The problem is the varnish on the solenoid piston rubs off and collects in the tube like housing and physicaly jams the piston preventing it from moving.
Curl up some 600 grit wet and dry, lube with oil and rub inside housing till all nice and clean, then do same to piston.
The put TALCUM POWDER inside and rub around , same on piston clean of powder, SPRAY WD40, let dry put together no more probs.
happens on VAUXHALL all the time only ever had to do above once on each car.
tabetha