SGS may be able to re-gas your existing struts, ask for a force of 210 Newtons. The problem with the Murena struts is that they are also used to carry the current for the rear window heater and not all replacement struts are conducting. I replaced mine with Fixed Force Gas Strut - F-SD02-250 from
www.strutsdirect.co.uk using the rod end eye from the original struts and a steel ball fitting SBJ8 for the tube end. It was slightly shorter than the original so the hatch does not lift quite as high (I've got the scars on my head to prove it!) and goes not conduct electricity.