Electronic controls shift and throttle

If set up right, usually very dependable. The ZF chrome bodied ones are good quality and last. Sturdy's are excellent. They do need constant voltage. I'm not a fan of the glenndenning ones even though CAT uses them on CAT 360 boats. Detents too stiff then throttle too light so you end up going into gear AND giving throttle when you only want to go into gear. CAT uses Sturdy on the non 360 boats. Don't get me wrong I run 150 different yachts a year, many of them during the first few times (engine start ups/ new boats) and have had control factors at least a dozen times over the last 15 years, but in general they're reliable these days.

Hynautic is reliable too, but has it's own issues. Resevoirs leak at the top seam after so many years, plugged filter in the bottom, bad actuators etc. But you can usually tell when something is on it's way out with them.

Stiff is usually the sintered bronze filter in the bottom of the resevoirs

I've always pulled the filter and cleaned them as I haven't found replacements easily. In your friends situation, I would simply plan on flushing ALL of the hynautic lines anyways, which the easiest way to do would be to fill the reservoir and bleed at every station to get all of the old fluid out. Start at the lower station first and then go to the FB.

distilled water is good and the recommended fluid for flushing hynautic systems. Be sure to use the correct fluid diluted to mfg. spec.when you fill and bleed system.