It depends how hard you are looking for the traces, it removes almost all trace. The RMA option will not delete recordings, the steps to get to an 'out-of-the-box' state would be :-
1) Webif >> RMA
2) Install Official firmware
3) Run Menu >> Settings >> Factory Default >> Format Hard Disk = No
"clean as possible" as in "no trace of custom firmware" (as implied by the reference to RMA) does not require a restore factory default operation. Just picky.
I might not have bothered, if the instructions initially posted in reply had been accurate in other respects. Also, in my opinion it is better to point people at the standard references than to keep re-writing them. It is no less helpful, and allows the effort to go into improving the references rather than allowing a variety of versions to be extant.
For the record - I wanted the box "as clean as possible" because I was trying to diagnose a number of strange issues.
In such instances a clean starting point for each test is essential. If I could do that and not waste time taking recordings
off the box (which dont affect the problems in this particular case) it would save me a lot of time.