BMW 1 Series Problems

 A 2018 BMW 120i Msport model can do 0-100km/h in 7.1 seconds.

Your car is out of warranty, so you would have to make a goodwill claim for BMW to replace the bottle free of charge. I think they should come to the party with the cost of replacing the bottle, and by all means try that, but I doubt you will be successful. There are many plastic components used in the cooling system on BMWs, and like the expansion bottle on your car they all eventually give trouble. In my view it's poor engineering.

The official fuel consumption figures for BMW's 120i on a combined cycle is 5.8L per-100km driven.

I would certainly consider this good consumption as many large cars use nearly twice as much fuel per-100km.

An older BMW I know of doesn't use any oil at all between services, but I'm told that it's quite common for the newer engine like yours to burn oil. It's generally held that a consumption of up to 1 litre per 1000km is normal. If you are concerned that yours might be too high do a check of the actual consumption. That way you know for sure how much it is burning.

The damage was done by one of the dealers, not BMW itself, so you have to work out which dealer it was that did it and when it was done and then attempt to negotiate a settlement with that dealer.

If you have solid proof of who did it then perhaps take it to the consumer affairs people in NSW and ask for their help.

That's a rather subjective question that's almost impossible to answer. It also depends on what you call fun. Both would be fun to drive, but if I were to make the choice purely on the driving experience I would choose the BMW.

The engine is probably worn and needs honing and new rings.