500's have had many changes over the years. Mine are much older than yours. I buy Baldwin filters on line by the case and have no problems. They come 6 to a case and are much cheaper than any yacht store. As I remember about $10 each filter last time.
I believe your talking about 4 micron and 10 micron filtration sizes. My tanks
are clean and I use a 4 micron as a primary filter and the secondary filters are all 10 micron which means they never get plugged. I still change the secondaries about once a year because they also collect any water
that gets by the primary filters.
I also installed a vacuum gauge upstream of the primary filters that show if one is getting clogged. Any reading above 0 is a sign of the start of filter clogging. The gauges come on most new filters. I buy my fuel
fueling places whenever possible because it's more recently refined and usually cleaner than the average small dock
. It's also cheaper.
My Racors could be 40 years old. Other than new seals
and new drain valves, they are original.