[Miker]

Does the 2008 2.4 transmission used a different size crush washer than the oil plug?

Since you performed the ATF and engine oil service both washers would be available to you to choose.

Is it possible you inadvertently used an ATF crush washer with the larger ID mistakenly for the smaller ID crush washer meant for the oil pan? I'm familiar with my 2013 V6 that has two different sized washers that I REPEATEDLY check just for this reason.

The larger ID of the ATF would fit looser on the engine oil plug, but would fit. When torqued to limits it is possible to deform it to a point where you might feel the bolt to "loosen". It actually might extrude the washer since there is less purchase area for the bolt flange.

 

[Miker]

OEM, only because they were the quickest to get into my hands at the time. So I got a quantity of each that should last the life of the car's oil/ATF changes !!

I would guess the DORMAN are at least as good as the OEM but even if it were more malleable I would think the seal would be fine.

Only other question I'd have that might explain a possible "stripped" thread feeling is if both the old (still stuck to the pan) and new crush washer was installed in addition and very few threads made contact during torquing. That would be a long shot, but......