I would also look into maybe the battery internals are the culprits as pleiades mentioned since you have no external current drain other than the 0.8mA you mentioned
So are you having issues with starting uo in winter time after leaving the bike unused for 25 days? or did I miss part of the thread!

BTW which model of CTEK do you use if it is the test & charge, then forget the test part of it; it is the same as a cheap voltmeter! A waste of money. But the charger is ace