just an idea....
To ensure this forum stays active, why not appoint a person for each MAIN THREAD. Meaning an expert for 3 series to log in everyday to answer or assist with any problems. This can be replicated with a 5 series expert, M Sport expert and so on.
If no questions arises, the expert may choose to post or update something new in the thread that he is responsible for. This wll give forumers a reason to log in as they know..there is always something new.
Just my thoughts.