The shaft that the spring clamps onto is already worn to a degree so time and number of "Weak" starts will dictate how much further that shaft gets worn down.   the fact that you have slippage is the primary indicator of the problem and failure is, I believe, predictable.  Some day when you're down for a few weeks just get the shaft and spring fixed and save trouble later on. The higher torque starters do much better and the prestolite direct drives are the top choice in my book for that job although people seem to be having good results with the ST-3 and ST-5 (better).   A weak battery, maybe small cables or long cable runs can affect the starting voltage and the problem can only escalate, not improve.  The shaft will not grow back its diameter.  I'm assuming nobody else out there has ISKRA starter and if they do it should be replaced given the history of damage that results.  As a separate data point, I do not need cross-tie with the prestolite starter and I have the same setup as you Adam, using Odyssey batteries.  I've only had to use the cross tie when a battery on the main failed and I could not start.