Dot 5 brake fluid

... as it seems to have most of the advantages of dot 5 without the disadvantages. I think there are good reasons why the manufacturers reverted to a glycol based fluid.

Don't!

There are no advantages to DOT 5 outside very specific high-performance applications. None of which apply to a Commando. There are considerable disadvantages to silicon-based fluids, like DOT 5, unless you meet the very high maintenance demands. Yes DOT 5 is kinder to paintwork - so don't spill your brake fluid or, if you do, wash it off quickly. More to the point, although DOT 5 has a higher boiling point, it is a disaster if you get any water in the system so don't ride your bike in the rain or wash it. And DOT 5 is more compressible so you'll have a soft, spongy brake.

DOT 5.1 is a waste of time and money  unless you are running a race bike and change the fluid at least every 12 months. DOT 4 has better minimum performance over the typical fluid change cycle of most road (or race) Commandos. If you change the brake fluid every 2 to 3 years like you're supposed to, any DOT 4 specification fluid will far exceed any demands your Commando can put on it. If you worry about stuff, look for a high-perfomance DOT 4 such as Castrol React which meets DOT 5.1 standards without the downside.

Would you ever use DOT 5 for a Commando? If your bike is going to sit unused in a museum for years without maintenance then, because DOT 5 doesn't absort moisture from the air, the insides of your brake system will not corrode.

The water will still enter the system with DOT5, the water will not be absorbed but will instead pool in the lowest spot, any steel at this point will rust and if the caliper gets hot enough the water will vaporise and expand giving a spongy brake.

My tip: strategically-placed wet towels make effective shields for your paintwork against misplaced brake fluid.

... you shouldn't use brake fluid from a previously opened container but I can see no justification for that as long as it's been firmly capped.