Help GL1200! I need a little instruction or advice

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Well it has been about six weeks ago that I bought this 1984 Aspencade 1200 that was in excellent condition only to find out it had a leaking head gasket. Head gasket has been replaced along with new belts, thermostat, fuel filter, oil and filter. Going to replace radiator cap, air filter, new coolant, and new radiator hose. My questions are,

1- is there something to put on the coolant drain plug to make it easier to remove next time?

2- do I use some sort of sealant on the radiator hose when I reinstall?

3- I also flushed the radiator with Prestone radiator flush because the temp was eight bars. I noticed when flushing with distilled water and the cap was off that water would push out the top. Is this because I maybe put in to much water. I want to get this right so when I go to put in new coolant I don't end up wasting a lot. Is this what is called burping? By the way temp is six bars now with extended idiling and the fan comes on also at six bars. Fan had a blown fuse for some reason but is working good now. Fuse was located under the seat on left side. Bike has 25,000 miles on it

4-Can someone supply part number for replacement radiator cap? Would something work from Napa Auto or some other supplier?

5-Is twenty to thirty minutes enough cooling time between distilled water flushes?
Don't want to crack a head.

Thanks in advance to anyone that can help out an old dude that ain't so sharp anymore.

Oldmanonavtx