Filters have been known to delaminate and go bad over time ( see
Howard Shapiro "Practical Flow Cytometry" for a discussion on the
subject)
barrier filters can be replaced easily but dichorics are a bit more difficult
due tot he positioning of the filter.
We have had good success in dealing with Chroma--( Paul Millman) .
I believe they make the filters for Bio Rad.
Robert Zucker
USEPA