If you're hung up on the RedLine products I'm sure the Manual Transmission Fluid they have will work fine.
This is not rocket science. Oil in a transmission does not collect contaminants as does oil in the engine. There is no combustion in the transmission (we always hope) so the particular oil is not critical as long as it is generally the right weight.
10W30, ATF type A, anything should be okay. I ran 10W30 Mobil One in my 240D manual with NO trouble whatsoever for over 300,000 miles.
The life of a manual transmission is much more dependent upon the skill of the driver than the particular lubricant that's poured into it. You want to get in the general viscosity range, but I expect you could put 10W30 weight, cheapest brand you can find, and it would work well, although since you only need to change it occasionally, Mobil One seems like a good investment. Worked for me.
Have a great day,