Your starter is a commonly used part- 10's of millions on the road
the gm "starter" has 3 parts:
1.) the solenoid switch ( the small canister riding piggy back on teh starter)
2.) the starter
3.) the "bendix" or starter gear
1.) the solenoid switch is damaged if trying to start with a bad battery or a bad connection- the low voltage will cause a "chattering" sound. with each chatter the interior contacts are arcing and pitting and carbon is deposited on a disk
easy fix- remove and clean disk or turn over to the clean side- clean good tight clean connections and condition of cables ( i've seen cables rotten inside the PVC insulation)
SOME replace with a remote solenoid, such as ford uses- easier to service and doesn't get hot
2.) the starter itself only has a few things to go bad- the windings, the bearings or the brushes- that's it. windings is fatal- brushes/bearing is dead easy fix.
the commutator some times needs to be cleaned ( with a hacksaw blade the mica is cut back)
3.) the bendix is the geared shaft which extends to engage the flywheel and then retracts once the motor is running- it is doesn't retract the starter will keep spinning even when the key turned back
this indicates a mounting alignment and shims may be needed.
make sure any shop warranties their work- so it is costly if they have a "return" or "customer come back" as they are using a good tech to fix the work of a crap tech
a shop will make more money selling you a new part and installing it
here is what replacement takes- quicker than brewing a pot of coffee
demand any removed parts
I've had many many vehicles and never a starter which couldn't be easily and inexpensively serviced ( except the right knee from kicking over antique motorcycles)- I have never never ever replaced a starter
I'm not expecting you to crawl under your van..(if you do disconnect the battery negative cable!)- just some info when you are getting service.
posting your location may get you recommendations for a shop