2012 135hp 3.0 mercuiser starting sometimes

Have a bayliner 175 with a 2012 135hp 3.0 mercuiser engine and decides to start occasionally. After taking out for a full day it will not start the next day and then is a lucky dip as to what day it will start. Nothing to do with carby and have changed spark plugs. Once it starts once for that day it will keep starting. Generally starts after playing with the spark cap and other times it doesn’t. Of course when we take it to mechanics it starts up and they think nothing is wrong. If anyone could help, it would be greatly appreciated.

The TKS solenoid is acting up.....