GL-4 differential fluid, not any combination of GL4/GL5, only a GL-4 rated fluid.
Factory manuals are located at
www.Lilevo.com/mirage/, looking up the 89 Colt/Mirage turbo manual will give specs for the 4g15 and 4g61t transmission fluid specs and quantities.
Most members running DSM and CSM transmission run Redline MT90 for engines putting out higher torque outputs, but otherwise a non synthetic fluid is fine, but again GL-4 rated (redline makes MT90 in a GL-4 specific blend). Synthetic fluid is always better, and only costs a few dollars more. Cheap fluids or the wrong mixtures can contain paraffin wax or somesuch additive that guns up the little fluid passageways and can therefore wreak havoc on a transmission. Mitsu dealers locally sell Diaqueen fluid but they bring it in by the 5 gallon pail or slightly smaller quantities, so unless you have a graduated cylinder/jug to measure with, I was out of luck in my case. Maybe US dealers fair better in that regard.
If you hop onto
www.Partsouq.com, and build your car, you can likely go into the transmission section and find the drain and full plugs blowup diagram and select those parts. Some parts like screws and washers can be listed with dimensions. If not, call your local Napa or Oreillys, or Kragen or whichever and ask what sizes of copper/aluminum crush washers do they have in stock. They cannot have the little rubber Inserts I see on cheap drain plug gaskets and they cannot be plastic!
Make sure they M12 through M22 in stock and you can always return what you don't use. I can't recall exactly the sizes in question for the two different bolts you are workin with.