Alternative to fill plug?

are you sure you used the right tool?

I've taken the shifter off and poured the fluid through there, as long as you know the capacity. And on my t5 I forced a smaller socket onto the bolt and now it's there for life, but that's because it was rounded off.

I've always drained trans through drain plug and refilled through shifter with FSM required capacity. One snap ring for me is easier than trying to find a good angle to crank that fill plug loose if I don't have the car jacked way up.

I know I could drain and refill, but I was trying to avoid having to buy another 2 quarts of Redline. The fluid in it is brand new as I just filled it less than a month ago and the car hasn't been driven since then. I guess I could try draining it into a clean container and re-using what's in it.

I forgot to add, it's also not as easy as a snap ring. I have an aftermarket shifter in it so I'll have to unbolt the whole shifter assembly from the transmission.

so if the fluid is new and only a month old, why change it?

As for your shifter, drill and tap in a fill plug

I don't want to change it, i want to top it off. It was leaking and I don't know how much fluid is in it now.

That's not a bad idea on the fill plug though. I'll have to look into that if I pull the shifter again.