Bag and strut are one unit thus you cannot replace one without the other.I have run over 90k on original struts as long as the bags do not go bad and the struts were still tight, moving freely,charged with gas etc..
if they are blown the car will bounce and porpus, or it will be rock hard if they are binding and frozen,
All I am saying is when the knocks rattle, clunks loose steering bad alignment etc started on both my Marks, I had 3 dealerships try to tell me my struts were worn out.
They were obviously wrong and full of BS.
Just dont want you disappointed if your trying to solve loose,wandering,rattling,thudd dddd dunk type noises coming from the front end. ON a 98 your struts should still be in good shape unless damaged or seals are blown, Not talking about the bag.
My 98 LSC has almost 90k on the original front struts, but I have replaced every other part down to the rack!