On my '95 E320 Wagon there are two "Airsprings" that hold the tailgate open. I think they are weaker now then they were then. What is the procedure for recharging them? I am considering using a pipe with end caps and an air hose fitting in one end. I'd put the airspring in there and fill it with high pressure air. It may leak into the airspring and recharge it. Whatdaa think?