B738 Hydraulic Quantity Inflight

[pre3l2s]

Last night flying at FL370, system A hydraulic quantity fell to 67%. When I first checked the hydraulics it was at about 75% and was falling 1% every 3-5 minutes.

I have never seen this before. Usually I check the hydraulics inflight and it is usual around the 90% mark at all times.

Once landed we checked the quantity which rose to around 90%.

I've looked in our FCOM and the only relevant info I can find was a cold soaked wing can cause fluctuations. Has anyone got any other information or anything from Boeing with inflight hydraulic levels for the B737?

Thanks in advance!