Go synth, and keep it for three months. But change the filter every 5000 miles. The synth doesn't break down, but it does collect soot, which willl get trapped in the filter.
The ABS master cylinder has electric solenoids in it to 'force' it to release the pressure. GM recommends using a special electronic tool to relieve the pressure from them before doing any brake work. But i haven't found a single mechanic who actually does it.
I make a special point of terrorising any medical staff that comes within reach of my family. They seem to get the point that anything that happens to my family WILL happen to them. They get real quiet and respectful awful quick.