Hell yeah the squate bottles of the “old school” testors is still around!!! My number one source for them? Wal-Mart baby!!! They are over in the toy section with all the plastic model kits (granted your walmart STILL sells plastic models!) All the places that used too dont anymore like CVS, Longs, Walgreens. Also Michaels has them as well, along with plastic model kits too!! Anyway the jars of testors enamel can be had for about $1.25 each at walmart and about $2 @ Michaels.
I get my “square bottles” from Michaels, using their weekly discount coupons. They are fine for basic colors like blacks and whites. Their basic yellow in the small bottle works as a fine “Cub” yellow. The paint in those jars is extremely similar to Model Master, just not such a wide selection of colors. Oh, they also make a “flat aluminum” in the square bottle line 
I’ve found out that stirring the paint, rather than shaking it, greatly reduces the potential for stuck lids. When I do run across paint on the rim of the jar, I grab a small piece of one of those “cheapo” foam make-up sponges you can find at some dollar stores in a bag and wipe the paint off the bottle right when I open it.
Don: Put the strap wrench around the cap not the bottle. ACESES5
I simply got into the habit of cleaning out the bottle and cap threads before I replace the cap. Once this has been done I don’t have to do it again, ever. The continual problem comes from shaking paint to mix it up. This coats the inside of the cap and creates the mess that needs cleaned up. I never shake my paints but instead use a Badger paint stirrer. If paint gets on the bottle edge for whatever reason I keep a paper towel handy and wipe it off before I replace the cap.