you wont need a new top cap seal every time, C2s tend to go on for ever, I have a set with pro levers that are just now, after 9 years beginning to feel a bit worse for wear, but a lever seal kit is cheap and they come back as good as new after a rebuild.
I normally try and replace all the seals at least every 2 years and bleed them once a year but somehow this set have just kept on going, I think I last bled them about 4 years ago :-s
They can be stubborn to bleed though, with some particularly awkward ones I have used the old magura 'reverse fill' method using a big-ass syringe on the caliper end and very gently but steadily purge it and just let the lever reservoir overflow. Its basically the same as what the C2 pressurised jobby does but filling from the bottom which can help dislodge stubborn bubbles in some cases.
Matt