I just said 'fuck the oil, there's a terrible event I have to grind through and I'm not going to screw myself over for it.'
Of course, the problem then becomes 'how often will we be in event mode and will we need to give up on completing some of them so that we can just get a roster of maxed tanks to do later events?'
Also also, I just redeemed two of my three concurrent factory 4*s as well, and it's been like nine total for me recently.