Not doubting anyones experiences or suggesting that the "big starter motor" ISN'T better than the later "smaller" one but I've never had a staring problem with any of the 6 small ones ive got
(and one of them I know for sure is the original factory fit and its nearly 15 years old
) I never had a twin battery set up in any of my transits either
I do agree that (like everything) they can eventually at some point get tired and renewal may be necessary and buying a reconditioned/exchange unit may not be the best option as replacing a few of the smaller (cheaper) bits inside might give it a new lease of life but the main parts (Field coils etc) will still be "tired" so it might not perform for long (as Fred was unlucky enough to find out TWICE
) The "Mechanical" properties of the materials change with Age/use/heat/corrosion and so the conductivity is affected
On a well serviced engine where everything else that can affect starting is in (near) tip top condition the length of time the starter motor is operating is reduced and therefore "longevity" is increased
I'll report back when my 15 year old little one eventually lets me down (but don't hold your breath)