You're absolutely right, the 507s when 1st delivered had some teething issues but this was at a time when the wirral line still had plenty of 503s.
Some 503s were transferred to the Northern line to cover for the 507s and from what I remember, the issues were quickly fixed and they were back in service in a far shorter time, however, this was before everything started to become far too technical because the more tech that is built into trains and other vehicles used for transport but for this thread specifically teains, the more problems that are going to happen.
As was pointed out in earlier pages on this thread, the introduction of the 777s should have been held back until all th issues had been dealt with instead of having to sort the issues out in service or during service times. If a fleet of new buses are not introduced into service until all issues have been resolved, why should it not be the case for trains, I have to say this introduction if the 777s has been the worst stock introduction ever, my apologies to anybody who doesn't agree but I am standing by my thoughts on this absolute farce.