The part is just a little plastic disk that can be easily
cleaned. It has small holes in it that can clog up and
the clog is what you want to avoid. You should not need a
new one (unless it was removed at some point).

I got one from www.volvoparts.com when I ordered a bunch of
other tune-up parts and I think it is only a couple of
dollars (easier to replace then clean at that price). But
if that is only part you want the shipping costs would not
make this a good way to go.

I don't see why a 98 would not have one.