Starter woes............

[1987BuickGN]

Dont know what its doing.......

Starter stayes engaged at times, even with key out of ignition. To get it to stop trying to crank engine over, you have to put key in, and turn key over like you are trying to start it again, with of course that dreaded cars already running starter crash sound. The starter is engaged to the flywheel turning the engine over, its not just the starter free wheeling on it on. This is my father in laws 1999 Chevrolet Express 1500. This is now the 3rd starter Ive put on in 2 days.

Is it,

a) ignition switch?

b) starter needs shimmed?

c) Flywheel?

d) missing ground?

e) battery cable

Anybody that has a suggestion it would be greatly appreciated. This thing has me Thanks in advance!