the back lift gate's hydraulic lift has failed. The strut on the rear driver's on 2007 GMC Envoy

side looks like it has leaked fluid/oil. How can I repair this? Also I had four new tires put on and the brakes checked. I was told brakes were fine but shortly after when I apply the brakes the pedal jumps and it makes a thumping noise. I keep my foot on pedal and when the vehicle comes to stop the problem disappears. It only does this intermittently. What should I check or what is the problem?

Asked by for the 2007 GMC Envoy
A lot of tailgate struts are only available from the dealer and are usually quite expensive. An aftermarket company called Dormin or Beck Arnley may make them. Regarding the brake issue does the ABS light come on? Could be warped rotors or contamination on the brake linings but it needs to be looked at as it could potentially be a safety issue.