The starter has for a while on my diesel screeched a bit either when first turning key or after turning over properly for a few seconds then a screech , this can happen four or five times before it actually starts, and needing more turns than it used to and at a slower pace.
So I searched and found some old advice from over 10 years ago, yesterday whipped the starter off used some carb cleaner on the copper solenoid piston and brush areas cleaned up the pinion end and sprayed with graphite dry spay , cleaned up all the connectors on solenoid and battery. The difference was astounding , engaged straight away , span fast , even started without heater plugs