97 antenna mast replacement

What special tool, if any, is required to replace a broken antenna mast on a 1997 Tahoe.
Mast bottom appears to have a round "nut" with indents at 12 o'clock, 3 o'clock, 6 o'clock and 9 o'clock positions.
Tried tapping around witha flat blade screwdriver and hammer but appears to be damaging.
Thanks for any help provided.
TB

The mast just unscrews from the base (like if you're going thru a car wash).

If it busted off at the base then an easy-out may be needed to remove the remains.

Otherwise there are no special tools listed in my '98 manual for removing the base hold down nut.

I had to replace mine with the same retaining nut. I used a set of needlenose pliers jammed into two slots on opposite sides, gripped good, and twisted slowly. Most "Universal" replacement kits don't reuse that nut so no worries trashing it while removing it. Worse come to worst, get a Dremel and cut two flats on either side to use a wrench.

I'll add that most of the plastic flat-angled bases that come with the new masts don't fit the curved contour of the fender (think I used the 45° one in the kit). I used a Dremel to cut it to fit perfectly. It takes some time to cut, check, cut, check, but it was worth it. The rubber washer that fits between the base and fender conforms to the shape with no problems. It looks perfectly stock if not better.

Hope this helps!