Do NOT interchange or replace fluids DOT4 for DOT5 or visa versa do not let them mix or even live in the same neighbourhood or garage shelf together ever.
If changing one for the other, 4 to 5 or vice versa God knows why anyone bothers to do this, replace all hoses and seals and make sure all the new components are compatible with the new fluid chemistry.
The argument that DOT5 will last for years in vehicles is partly true the fluid will last for years and does not absorb as much moisture as DOT3/4.
The components/seals o-rings, boots however don't care much about fluid type, they just don't like not being used,they sit about stainionary, drying out and deteriorating, awaiting the first time the owner slams down the brake peddle or pulls hard on the lever, to say, "cheerio" see you in the morg.
So why leave a fluid in a vehicle for years?
Change fluids regularly and exercise your brake components regularly as you would your favorite sheep.
The fluids are very different and have interesting detrimental possibly lethal effects on braking components when mixed... or crossed over.
Change ALL your fluids regularly it is the law, it is cheap and it means you and or your machine will not die.
Stick to the fluid designed for the system and check you use the correct fluid every time.
You would not leave the same engine oil in your bike for years why do the same with the system that stops you from dying.
It is easy it is cheap, did I mention how cheap brake fluid is, change it every year if you can be arsed.
Saves time on stuck and deuteriation of system parts and it may keep you above the sod for another summer of riding.
On the bleeding you have a problem.
It it could be the following stuff, the master cylinder, if you cannot drive fluid down and out of the caliper furthest away bleed valve I suspect you have poor lever hydraulic pressure,restriction,blockage,seizure..
Suspect One -Master Cylinder Seal
Suspect Two- Brake line/hose hose condition, was the fluid removed black? if so dump hoses immediately and replace with lovely goodridge ones.
Suspect Three- Check the pistons are moving freely in the calipers back and forth, if stuck then there is another reason why bleeding is poor.
Suspect Four_ Check condition of caliper piston seals cost pence have them replaced by someone competent.
Use a professional, brakes are nasty dirty things they mess up are lovely vehicles wheels but there functionality will without doubt stop you from a premature death.
Rant Over.
Love your brakes look after them they will look after you.