Very welcome, it is not too hard of a job to do, sometimes that modulator is repairable, but it may need replacing, a GM Dealer is going to take a chunk out of your wallet for it, not sure the actual price.
I am pretty sure the modulator is somewhere behind the glove box, getting to it is the hard part, will most likely require somebody to get upside down with feet in the air to get to it.
If you take it in have them inspect all vacuum lines, even any soft ones coming from the gas tank, on my 96' Park Ave I recently had to replace every soft EVAP hose, even the ones for my rear air struts compressor/air dryer, they were all deteriorated/dry-rotted.
2006 Pontiac Grand Prix GT with SC
1996 Buick Park Ave NA