If I recall the rules - no,he does not have to start,but he has to drive at some point during the race,otherwise that would be unfair. The minimum distance I don't know though,might be even just a lap.
Button clutch was never a topic in the context of OEC and it was never forbidden explicitly. The rulebook you looked into is still the one of OEC III. There also was no passage about BC in the rules of OEC or OEC 2. I simply was not thinking of it when the league ran the last time and pretty much forgot about the issue in my hiatus.
The rulebook still needs to be worked on as e.g. the skin rule is still punishing those who drive without skin instead of awarding the extra point to those who drive with skin.
I have to look for a way to detect button clutch first, that does not involve watching every entries 3 hours. A rule means nothing if it cannot be enforced.
EDIT: By the way, can anyone brief me on this topic? Back when I was in the CityLiga admin team we discussed that topic immensely, but this has been quite some time ago (and equivalent discussions in the mists of Genuine Racing events or even New Dimension Racing events is even longer away) and most of the discussions happened on TeamSpeak anyways. Is it correct, that the advantage a button clutch gives comes from a makro used to decrease shifting times rather then just the usage of the option button clutch? Then the only option to check if a makro is used was to check the shifting and evaluate if it was short or normal, before later it was decided to simply ban the button clutch option as the makro was incompatible to automatic clutch and axis clutch respectively. So everyone who receives an automatic clutch flag in the mpr (using mpRes or similar) was fine and those who did not have that flag were looked for the usage of H-shifting, who were also fine. The rest was penelised.
Auto clutch takes around 0.1 second more to shift than a button clutch with button control rate set to 10. You can still shave a few hundredths off by making it a macro in profiler or autohotkey or w/e you want to use for macros. It's an unfair advantage in some combos, especially with UF1/GTi.
IMHO, a button clutch should be allowed only if it is done without the help of an external software. This, however is almost impossible to notice without taking time to look through the replays, as airio and other LFS stat softwares notices what kind of clutch you're using, but it doesn't go much further.
https://www.lfs.net/forum/thread/45980
Here's some discussion from a few years back about the subject along with some experiments by some experienced drivers, if you have time I suggest to read it.
That being said, would it be possible to fix the airio path on the server, by the way? The !top leaderboard doesn't work at all, and it gives out invalid path every lap. I'm sure airio has a path file for KY21, now it seems to have the original KY2 path
Please note: I was away a couple of days, hence why there are still some teams unapproved. They will either be approved or notified what has to be changed today.