All good points made by member Zunspec and I'm getting a vision
, another possibility. Maybe it's me or just the lighting in the pictures but does it look like there may have not been a continuous bead of sealant applied or it was breached when engine went into service,especially on the wall that separates the transmission from the crank chamber and maybe none applied to critical areas around the oil channel(need a very fine thin layer as not to have excess squeeze into channel) to the center bearing oil port. Type of sealant used? Mating surfaces completely wiped down with acetone or the like before sealant applied? Transmission filled back up with oil and engine started before some sealant that is not even suppose to be used for this purpose had reached its curing time? Upper and lower case bolts torqued to the proper values and in order as per the number stamped in the case near each bolt?
Some do a pressure and vacuum test after installing new inner and outer crankshaft to test if there are any breaches in a cured seal. It's possible you can hear a leak/breach(muffled hissing sound)coming from a pressurized crank chamber by removing the oil fill plug and putting an ear close to the hole.
Obviously, what I'm getting at is that maybe, just maybe, transmission oil was being sucked into the crank chamber maybe by the drop or even just as a mist during those 500 miles you rode.
BTW, were those 500 miles highway or city miles you put on the clock?
Bloody shame about the damage and buying a transmission off ebay can be risky if only that it can be so hard to see any telltale evidence of flaws/damage and the degree of wear on all driven gears and gear wheels even with a lot of pictures.....been there....done that. Best chance of course, if the price is reasonable enough to gamble on is to wait and see one listed as low mileage and taken out of a later model T or GT500.
There is a 4th gear driven listed on ebay....been listed a long time by a 'certain' seller that says it's NOS but at that price and by the picture....I'm just not 100% sure it's NOS...I could be very wrong( I'm slowly putting a spare driveshaft together with NOS gears and wheels) but I'm in no hurry to gamble on it. 'Somewhere down the road', I might wind up buying at least 4th and 5th driven gears from and maybe send a counter shaft to one of the companies below for 4th and 5th counter gears.
You may already know about these companies but just in case you don't....
http://www.novaracing.co.uk/ProductSuzu ... Gears.html" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;"
I don't know for sure if he is still making gears and I can't find a link just now for Moore Engineering but there is reference to both in this thread....
viewtopic.php?p=87359" onclick="window.open(this.href);return false;" onclick=
Again, sorry about that mess and good luck ironing out the issues.