Hello,
I will be glad to try to help you. I am also happy to tell you that your 335i is one of the lowest oil consumption levels that I have seen so far. 12,000 miles for 1 qt usage is amazing. BMW states that 1 qt per 750 miles is the accepted level. I have seen around 5,000 miles to 8,000 miles is the usuall mileage for 1 qt.
What an amazing vehicle the 335i is! Since you have been driving in a tame manner that explains the low usage of oil (by what I have seen and BMW's guidlines). The dealer would be happy to top it up for you before the next service free of charge if they are close enough for you to get to without much trouble.
Please let me know if I can clarify anything. Please accept this answer. If you could leave a short poitive comment on feedback it would be appreciated. Thank you.
BMW Mechanic
Level 1 BMW Master Certification, 9 Years Dealer experience, Team Leader, Shop Foreman