I'm going with foama's suggestion: it's mix & match time!
I bought 1 QT of Royal Purple 100% synthetic Synchromax manual transmission lube. It's recommended for manual cars that use ATF.
And I bought 1 QT of Redline "MT-85" (Redline says it's 75w85). That was the lightest non-ATF gear oil available at my local parts store. (Mitsubishi calls for 75w80 for our cars.)
Between the two of them, I'll end up with something less than 75w85.
Just for fun, I'm going to do a simple pour test to compare how quickly a measured amount of each oil drains from a container with a small hole in it. I'm also going to also test what's in the transmission now.
The transmission oil is draining as I type this.
The oil that's in there was pretty thick; hardly any ran out when I removed the drain bolt (ambient temp around 5C / 41F). For a moment I wondered if the transmission was empty! I had to remove the fill bolt to get it to drain properly.
I have already referred to the following very helpful thread for locating the drain/fill plugs and other helpful tips:
Thread: HOW TO: Changing 5MT Gear Oil (Manual Transmission)
Will post results later. I should probably start a new thread.
View my fuel log 2014 Mirage SE 1.2 manual: 64.5 mpg (US) ... 27.4 km/L ... 3.6 L/100 km ... 77.4 mpg (Imp)