A/C wasn't blowing super cold, so I attached my refrigerant can with the cheapo gauge and it was in the green, so didn't add any R134a. when I removed the attachment from the service port (low side), I could feel that it was now leaking. It was very minor, but now I need to replace the valve. The system is charged, so I'm looking at using the Mastercool 81490 R134a Valve Core Remover Installer that allows you do this without evacuating the system. Youtube videos showing folks doing the replacement make it look like a snap on other cars, but if you read the reviews of the tool, tons of complaints - However, I think that it's from people that didn't know that there are different size valves and bought the $35 tool when they needed the $80 that does standard, JRA's, and R12. Specifically, some complain that they backed off the valve, but then it's too large to fit through the tool opening. My hope is someone knows with certainty that the Mastercool 81490 works on a 2005 Yukon Denali. If not, my backup plan is to buy the tool, go to the dealer and buy the valve for my vehicle and make sure it passes through the tube before actually trying it on the vehicle. Yes, I know it won't work on the high pressure side, but it's only the low side that's leaking. If you think that evacuating the system is the way to go because the system would benefit from fresh oil and refrigerant, I'm interested in opinions too. Here's a video of the tool being used.