Hi Dison911,
It may be too late to reply your question. I had the same issue and got the both air spring replaced. Now it coming to 2 years after the air spring replacement. I bought the air spring from Alibaba supplier with the DAP Malaysia cost at about RM660/-.
Please also check your Vanos system as it is known to have screw breakage issue. I had mine checked I encountered cooling leaking issue. I have a road lengthy of story to tell to manage this beast.
We can exchange experience as not many 5GT in Malaysia.