1) I don't see any problems with the 25k drains. They're probably relying upon an oil vendor, not the manufacturer's recommendation. The minor varnishing is of minimal concern.
2) Going to 5k intervals is a complete waste of time/money. At best I'd probably use a full synth HDEO like Mobil Delvac 222 0W-30 / PetroCan Duron 0W-30, etc., with its diesel additive pack to clean that up. Instead of whatever additives he's proposing.