Jinma starter problem

For many months now my 6 year old gear reduction starter on my 254 Jinma has been inconsistent.
It has slowly increased its failure to stay engaged with the flywheel. It initially engages but then disengages. It averages about 6 start cycles before the pistons are in the right position to start because the starter disengages so often that the flywheel only turns 1/3 turns or less.

Also about twice a year this starter has a separate problem.
When initially trying to start the engine the starter stays in start position even with the key quickly disengaged. I have to jump off the tractor while the starter is turning over and stop it at the emergency knife switch controlling the ground post on my battery. Initially I suspected the contacts in the solenoid were welding themselves together and creating the problem so I unsolder the solenoid leads to dissect the copper contacts. To my amazement everything looked average. Very little wear and no burn spots were evident.
I notice the return spring on the contacts connected to the rod that is actuated by the solenoid plunger was collapsed so I expanded the spring by 1/4”. And I greased and chamfered the contact rod.
Upon reassembly the starter seems to work better but only time will tell as I feel I haven’t really analyzed the problem.

[spring might be fatiuged to the point that your streching will be a temp. fix, but it will give you the knowledge if that is the issue with the starter]

I also think the shaft that the solenoid plunger  forces forward to engage those high amperage contacts is not  quite long enough to keep it from cocking sideways and initiating the start sequence but not continuing that start sequence.
That also might explain the second problem of the starter running uncontrollably because that shaft is not returning to its original non start position because it is bound it its bore. Higher spring pressure corrects the problem by forcing it back into the non- start position.
Agreed that it is only a temporary fix.