FS-2500, 20,000 miles between oil changes, oil samples and new engine filter every 5,000 with make up oil, oil sample every 5000 miles and the report says I can usually go further, but I don't. At 20,000 miles you can still read the dipstick. The truck has 170,000 miles and I put it on at 40,000.
I have a Amsoil partial filter on the Jetta, samples look ok so far at 10,000 miles, but the oil has turned black. It has only been on for 10000 miles. I am not impressed with it, but the only real option for the VW TDI engine.
FS 2500 runs about $600.00 now with their filters at $30.00. I have run the FS 2500 to 40,000 miles once, but I m back to every 20,000 for changing it now.
I use Mobile Delvac 1 and a additive called TX-7.