GM-GMC: 454 Engine and starter, flywheel teeth, lifetime warranties

Question
Thanks Harry.  I did exchange the starter.  There were 2 options, one had a larger housing and opening than the other.  Since the larger one failed, we tried the smaller one.  It works but the guy helping me install it said he thinks the flywheel maybe be going bad.  The teeth were not the same size across the top of each one.  We did not have to shim but I did get some shims from the auto parts store.  What should the flywheel teeth look like?  How do I know if I need to shim?  Thanks for your help so far.  Tony

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Followup To
Question -
I recently bought as 1986 Chevy Sierra Classic 3500 with a 454 4b engine.  The prior owner said he had a few issues with the starter.  He has replaced it once already.  The replacement starter now seems to have also gone bad after only 3-4 months.  It wines but does not turn over.  The battery has over 700 AMPS cold cranking power.  Any thoughts.  
Answer -
Tony,

GM has always had issues with their starters and they generally occur in two categories:  Heat and gear teeth.

The solenoid, being positioned on top of the starter, is very close to the exhaust manifold.  Over time, many solenoids fail from the extreme heat they experience.

The teeth on the starter drive and flex plate (or flywheel) will wear quickly if there were any shims left out when the starter is changed.  Not all GM engines have shims, but for those that do the shims are critical.

Many auto parts stores carry starters with lifetime warranties.  I would buy one and put the receipt in a safe location.

Answer
Tony,

The flywheel/flexplate teeth should all be even and undamaged.  It is not unusual for teeth to be missing or worn half down on GM engines.

Whatever wear you see will be transferred to the starter drive teeth in time and cause problems.

This is a common GM problem.  It's a pain to change the flywheel/flexplate, but your starter will last longer and your vehicle will start more reliably if you do.