I also have the same treadmill and the silicone oil supplied is very economical and lasts a long time. If it runs out, I would also use a silicone spray, e.g. WD-40 silicone spray would be an option. (also available in the Galaxus store;).
Ps: if you don't want to spray it directly over the spray can, you can spray the spray into a container and then apply the oil to the belt/roller.