Hey Doc,
Running other brands of oil in the ETEC is penny-wise and, well, you know. Stick with HD-100.. 'nuff said.

Two options for reducing the cost of the oil.

One: as Bucket suggested keep your empty jugs and buy bulk from your dealer.

Two: If you're committed to your ETEC for the long-term as I am then consider the purchase of a 16 gallon drum. It will be the last time you'll have to think about oil for four years at your current useage and when it's empty you can refill it from your dealer's drum!
Think of it as one big jug!

This is a great time of year to get this done as most dealers have oil buying incentive programs around show season.

Good luck, T