I'm beginning a major service on my 1988 K100RS and starting with a coolant change. I have been reading on various sites that Prestone long life concentrate with distilled water is a good choice . I'm trying to avoid using BMW coolant and paying extra for what? Has anyone used this Prestone or similar stuff and if so how did it work out.

This easy is easy to find at Wally World (WalMart). No problems after many years of use (and changes) on my high mileage K100RS.

I have used it with no bad effects.  Also used Peak and NAPA coolants as well.

I'm pretty sure any universal Long Life coolant will be compatible with the Brick's aluminum engine.  What I understand is that back in the 80's when the Bricks were first introduced most coolants were formulated for cast iron engines.  Today, aluminum alloy is almost universal and the formulas have been changed to accommodate it.

The price of the coolants at Walmart is low enough that I can afford to change it every two years, further protecting the engine from corrosion.

Thanks ! Now I know .I didn't want to just do it and regret it later.

And....
coolants come in GREAT colours these days!  

I've been using OEM coolant with distilled water for 20 + years & 180,000 K's and I'm still running all original cooling system parts. I have coolant test strips and change the coolant as required. I've flushed it a couple of times and found that the flushing didn't flush out anything and was a waste of time. In preparation for another coolant change I bought a bottle of OEM coolant to find that it has changed to Lifetime coolant. I was paying $16.00 Au a litre for the BMW coolant the lifetime coolant was $24.00 a litre. I have yet to use it.
Regards Martin.