Sounds like a repair very similar to what I recently did with my Aptus 75. The price is the same as mine (pricing should be standardized, i e almost exactly the same regardless of dealer).
I think they will replace the "e-box", i e all electronics except sensor not just the firewire board. If I've understood correctly that is how the back is designed. If some electronics breaks, you replace the e-box, not just some single component. It feels a bit pricey for such an old back, but what you get back is essentially an "as new" digital back with fresh electronics so it's a quite okay deal.
Service time seems to vary *a lot*, and depends both on dealer and Leaf factory (and if you live in a remote area like me the courier
, it took almost a week extra for UPS to deliver the back to me). One must be prepared to wait quite some time, I don't think repair of old backs is the top priority.