I cannot find a dedicated cycling forum, if there is one, mods please move to it.
I am getting repeated slow leaks developing in the same place every approx 60 km. It is always along the seam which runs round the inside of the tube, ie, that part which is in line with the valve and in contact with the rim away from the tyre. Therefore, it cannot be a penetration from outside. It is always just a few cm. from the valve. If I repair it, the puncture recurs in a similar place about one cm. further along the seam. After 3 punctures I replace the tube and it happens again. I have replaced 2 tubes so far.
I cannot find any flaw in the rim tape but I have reinforced it by wrapping plastic electrical tape round the rim on top of the rim tape. The tube still punctures.
This is totally outside my experience, can any cycling fanatic suggest a cause and a cure. Additionally the tubes have all been from different manufacturers so it is unlikely to be a bad batch of tubes.