Racor 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 at
commercial 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.