The only incidents that I have heard of have been on this site.
I personally have had the cables off dozens of L 01 series tractors and have yet to damage an ECU.
I also have had 2 units hauled in after the owner changed their battery and installed it connected in reverse polarity. Neither one...
They are SAE, 5/16" if I remember correctly. They should have had a nut and lock washer on each bolt. The bolts go through the valve; there are no other plates.
Remove the alternator or dynamo, remove the 4 shroud bolts, and move the shroud towards the engine.
Remove the upper and lower radiator hoses from the radiator, and remove the 2 hairpin clips from the radiator mounting pegs below the support.
The radiator will pull up and out.
You need to replace the shaft, pulley, feather key, bearings, and shaft seals.
Once the pulley gets loose on the shaft, it wears very quickly, which causes the pulley to run crooked.
Your problem appears to be more a dealer problem than a machine problem.
If your problem is with an emissions component, those are still covered under the emissions warranty for a few more years.