Bro, you talk like a lawyer? Your words very chim! Well said!
Anyway all motodiam wants to make some profits out of what they sell. To compete with their competitors, they offer all sorts of free gift to attract all those 'kiasu S'porean'. Free gift is not actually free. In fact, you already paid for all that stuffs.
In short, When you try to sue them, they will use all those free stuff to cover back all the extra percentage they've charged you when you purchase the bike. Because nothing of the free stuffs were written in the contract nor receipt. Unless, like you said, recorded conversations and witness are the strong evidences to testify them in court. But who really wants to make a big fuss on this. It's money and time consuming. These are what almost every S'poreans dislike.
If you win, maybe you will get the bike for free. If you lose, your lawyer still gets his fee. So, for my personal opinion, if you want to do all these for an RXZ bike, is not worth it. For a turbine powered Rolls Royce Y2K, I must say YES! I want to be your witness! Hahaha....