Hi 57rat,
Welcome to the site.
I always heard that the oil bath air filteration system was like 95% or 98% efficient. I have always used them especially if I was lucky enough to have one equipped with a new vehicle purchase or found one available for my particular application. The big plus is, they are easy and cheap to maintain and I think they look way too cool. Just my opinion.
If you are thinking of a replacement, spend the extra money and go for the K&N as was mentioned above here already. They are without a doubt among, if not, the best replacements available.
Dave
