HelloCustomer What are you trying to accomplish and what is the year, model and engine size of your GMC?
Your JA Expert,
Oh, boy thats a rough one. I've been using this product and have seen the most incredible results from it. Not like anything else I have ever used. I have had fittings completely siezed where I could not budge them with a breaker bar. I sprayed this penetrant, wacked it with a hammer and it freed up immediately. It freezes like dry ice and allows the penetrant to make it's way in as the metal contracts. When you wack it, it allows the items to break free. Wear protection since if this get's on your skin or eyes it could cause some damage. If anything can work, this is it. I hope it does the trick.