Alko air bag suspension

Hi everyone, I have just discovered my offside rear suspension air bag  on our LWB Peugeot Boxer based Kemerton is leaking, one of the fixing bolts has chaffed a small hole in it even though I check the pressures on a regular basis so they have never been run low on pressure.
A couple of questions :- 
Has anyone replaced the original Alko bags with after market units as advertised on e-bay, if so which ones and do they appear to work ok.
If replaced with the original Alko bags where is the best place to purchase them.
Thanks in advance for any help, Bring on the summer


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Had one of mine replaced last year by Mill Rd Garage,Christchurch.after going over a low drain cover,labour £160 parts £318 plus vat,a very helpful company not far from you
Run by Mike Roberts and Olly