Dead End Redux: NOW, with new and improved Purple visor action!

And just because I was starting to make good progress, I just had to go and muck up a couple other things. At least these should be easy fixes.
Been going to work on Alt Sunstreaker. Here's his new legs so far.

Seems like when you lay a coat of enamel over a different coloured coat, it strips it. Actually even over the same colour, noticed it first laying down a second coat of the gold and then when putting the yellow over the gold. Is that just a case of the 1st coat not bonding to the plastic?
And my current technique is to paint a bit too far then clean up the mess after. Which is probably a bad idea in the long run. Been trying the tooth pick technique as well, but having a tough time getting the paint to where I want it. Have to redo the stripes on the lower leg.

Put red in the cracks then tried to paint lightly over the raised in yellow. Was so thin tho, it just flowed into everywhere, as you can see on the left. Tried scraping the grooves to reveal the red on the right, but didn't wait for it to dry. Which just turned into an orange mess. Anyone suggest another method, or should I just work more carefully, lay down one colour, then fill the gooves once its completely dry?
Last thing for now

, is there a way to clean up the streaks after taking off paint with isopropyl?
Thank you all again for the help