And my 2-Stroke Yamaha's user manual prescribes using Yamalube motor oil.
Whereas I use Shell!
The reason companies prescribe their own products is to enhance their sales. Using oil / coolant / filters etc from a third party source won't affect the engine; at all.
Just flush the existing coolant and add whatever coolant you feel comfortable with. NEVER 'mix and match' coolants as it might cause a negative chemical reaction that might ruin your radiator.