2002 GMC Envoy Suspension air pump

I have a 2002 gmc envoy with rear air suspension . The compressor runs but no air to bags etc.I have read the GM service bulletin #02-03-99-001 regarding the service kit. I obtained the kit #15183676 from GM. Have the compressor out and trying ti remove the 2 screws holding the compressor head. Being in Minnesota's harsh winters of 6 months of snow slush SALT etc , the screws will not budge. I am afraid if I get to aggressive I will either strip the torque heads or twist the screws off.. Do I dare use heat or ? to help loosen. Don't want to ruin the compressor ..What next ???