Filling transmission through check plug

I would like to verify the fluid level inside my transmission but don't want to drain/refill (it only has a few thousand miles). The drain gasket for the fill plug is on back order with no availability date so I would like to avoid removing it and having a small chance of leaking with reusing the gasket. I was able to get gaskets for the check plug. So my question is: can I use a syringe to "fill" the transmission through the check plug? My process would be:

1. Remove check plug from COLD transmission.
2. Pump in fluid through syringe until it flows back out. The transmission should now be over filled.
3. Replace check plug and run the standard fluid check procedure. This should heat the fluid and drain the excess to the right level.
4. Replace check plug with new gasket.

Not sure if I am missing anything or if there is something above the check tube in the pan that would prevent me from getting my syringe tube up in there. See attached drawing for my idea.

Thanks!

 

On my 2010 Tacoma I didn’t change the o ring and I filled through a passenger side port. It should be there on the Runner since it’s the same transmission.

 

I would check it without adding/wasting fluid. Fill plug gaskets are backordered? Use aftermarket or re-use one that's on there.

 

Fill plug shouldn't leak without a gasket. Fluid is below it. Reuse it. As long as it has one is main thing. I don't remember mine having one on fill but probably wrong. You can let it run with plug out while filling, which is what you should do to fill transmission cooler and lines, none will come out.

 

I don't know its kinda tricky