I wasn't sure if my little Gasser (that I bought in November) had a decent mix of antifreeze, since I may need to store it in sub zero temperatures sometimes ... well, I drained it and what was in there came out full of crap and obviously ancient

I'll be changing it again after the next time I've ridden the bike, to make sure it's well flushed.

The moral of this story - don't believe the person you bought the bike from when they say that it's all serviced and ready to go!

Generally, 'all serviced' just means they changed the oil every so often and, if you're lucky, cleaned the air filter. Always assume a used bike has been treated like garbage. Change the coolant once a year.

Indeed, I'm working my way through the bike so when it's time to move up to something bigger I can sell it and honestly say that has been taken care of, lol

I agree used to often just for oil change, air filter, and chain clean and lube.  It often doesn't include checking and re-greasing things, coolant changes (as already noted), or checking of loose bolts etc.

Good luck.

I dunno, I've bought bikes (and cars) before that have been exactly as described, where the previous owner has done regular maintenance ... in this instance the bike has been performing great, so I'm a little surprised they missed out on that part of the servicing

When I purchased my used Ossa 280 it had 65hrs on the clock. The prior owner used distilled water for coolant, which was said to be a season old. Since I often travel into areas that may fall below freezing I opted to change to Engine Ice (which I still have a bit of from snowmobiles and enduro bikes). 

It came out a bit cloudy, once I allowed it to settle overnight here's what it looked like. Although I've seen worse I'll rest easier knowing its freshened up (and freeze protected).