As far as I know...the D15's and D16's according to the Helms Manuals just say to use 10W-30 motor oil. About 2 quarts I believe.

B16A's and B18C's were suggested to use Honda MTF. 2.5 quarts for the B18C's. Honda MTF generally runs about 5-6 bucks retail per quart. You dont need any of that fancy stuff...and is often suggested that you should not.