You will find most gas struts fail eventually, through use. You dont mention how old the van is,my Heki rooflight is 16yrs old as the van and still works perfectly. If the roof light is open and is forced down by really heavy winds that does not do it any good. Fortunately they are easy things to obtain and fit.
We use leisureshopdirect (other specialist parts sites are available). We found them helpful; good diagrams too.
They also had a technical person who replied directly to complex DIY we had, like changing spring-fit window blinds.
As well is two words!
How does a sage know everything about everything? or does he? or does he just think he does?
Remember, if you buy something you bought it, not brought it.