Yeah, this has screwed me before. I would just leave the lid off the bottle till I was done, now I try to cap it as soon as I fill my syringe.
I have Guides on both of my bikes and haven't really had any issues, but they do seem to require a lot of maintenance. I blame the mountain creek moon dust but most of the time I have noticeable problems it ends up being sticky calipers. Also, sintered pads. I wear through orangic pads so fast it feels like I have to readjust or bleed after every other ride. I didn't think about my last bike coming stock with organic pads and just thought the brakes sucked. After switching pads I rarely have to touch them besides normal maintenance.
All of that said.... I do want to try something new. Probably gonna go TRP on the enduro bike.