I have a couple of classic cars, a 1934 Plymouth with a chevy BB and a Lincoln Continental. These cars get driven about 500 miles a Year. I live in a rural area of Southern md and these cars see very little stop and go and are taken out oun nice days and to Car shows. I use synthetic oil in both cars. How often do I need to change the oil and filter. With these new synthetics I've seen some very long oil change interval in newer cars. Is it realy necessary to change it every 3mths or 3000 miles?