Would appreciate any help you can give about replacing the booster yourself. I may try to replace myself if it doesn't seem too difficult. However if I screw it up I don't have a car to drive so that may be a deciding factor. Thanks!Update after almost a year with this annoying ticking/clicking noise:
1) I ended up by replacing the iBooster two times, both times with a used one. I did everything by myself. If you need advices for the replacement I'll be glad to help you.
2) I disassembled the original iBooster to inspect what was wrong with the internals. Mechanically everything looks in perfect condition, no signs of wear of any of gears. So definitely the attached electronics or the attached position sensor failed. You can change this sensor but to do that anyway to have to remove the full brake booster first to gain access to it.