335's are like a moded 328i. with the increase in performance you do get a bit more fragile engine. In fact, the higher performance (output ) this is usually the case.
Example: Owned a classic 911 and it was great but they need funds to keep going. I knew that going in and was cool with it. Had my fun.
335 is a lot of performance for the money. CPO gives you a few years but is not the end all to a trouble free/expense free existence.
I decided to not enter into the 335 goodness but still enjoy all the dynamics with a 328i with sport and mt but its not as fast. 335 is a blast to drive no doubt but it comes with a price. You have a better chance at reliability with the 328i but you get a trade off.
Many have NOT had nightmare problems with the 335. Good luck!