If its like my 84 Riviera, you have to loosen the front fender to get it out. Do yourself a favor and see if you can find the factory instructions. There are several steps that have to be done in the correct order to make the job work without ruining the fender or door. You might be able to subscribe to alldata, thier info is usually the same as factory.
You have the remove the bolts at the rear of the fender and the bolts for the inner fender and remove the ant . assy.from the bottom .You then drill out the rivets to seprate the motor housing to replace the ant.
mast assy. You will want to wear a long sleeve shirt when you do this repair or you will look like you were in a cat fight
I just replaced the antenna in my 87 Lesabre. I just replaced the bad one from one that i bought at NAPA for fifty bucks. You will have to get a universal Antenna conection to fit the GM one when you disconnect your old anteena. :beers: