Well after a 6 pack and a hack saw...I got the new bottom mount mini on. Hopefully I can pull off a you tube deal here. I can't figure out why the pinion on the starter is going back and forth(for lack of a better way to describe it). I think it may be too tight against the flexplate. Would that cause this? Bad flexplate?? Also do they make a thick or maybe a tapered starter shim. Right now I have the 2 shims they supplied with the starter under the inside bolt only.
the flex plate might have a little too much wobble to it, I had the exact same issue a couple of years ago. I changed out the SFI plate I had and put a better quality one on and haven't had another issue yet.
Looking at this video you made-
there is some wobble there although mine was a little worse.
Ive had the same problem. As long as your sure you have the right starter and flex plate combo (cant really go wrong if) Cut a shim or 2 in half and stack em on the inside bolt. Put a full shim in then two or three half shims on the inside bolt. Worked like a charm for me. Id be affraid a full washer mould be too far away and might have a problem with stripping the flex plate. Just my .02
Fwiw I just bought a 6 pack of starter shims, installed every one, and was happy with how the gears meshed. How ever it does the same thing. I tested my cranking voltage with the multi meter on 10v, and it would dip below that(9ish). New battery time?