I had a puncture today and due to having to faff around with a dodgy inner tube where the valve core kept unscrewing each time I unscrewed the pump head, the bike was upside down for about 30 minutes.
When I checked the brakes after righting the bike, the front lever went straight to the bar but pumped up to normal after 3 or 4 pulls (the rear lever was fine but has done the same in the past); the brakes functioned exactly as usual from then on (including coming down out of the Mendips). They’re SLX brake and about 5 months old (came pre-bled but I just cut the hoses without re-bleeding).
Is this an indication of air in the system or normal behaviour? Pumping the lever back up felt the same as finding the bite point after having pushed the pistons back in but the front wheel never left the bike.
If I do need a bleed I assume that I could just ziptie the levers back overnight and top up the system from the lever.
On a related point, I have an old 1 litre bottle of Shimano mineral oil that probably 4 or 5 years old. There’s no indication of a use before date on the bottle and it’s been stored sealed and in the dark (as per the instructions); can I use this to top up or bleed?
