Re-filling the air conditioning isn’t quite the same as having a new part fitted – if it leaks out, not everyone will re-fill it again free, under a limited warranty… and in between losing the gas and re-filling it again, you may have to pay for investigation time and repairs. Here are the main components that can cure leaks (try eBay).
PS Do check your Bongo’s air conditioning valve types. One of my identical pair is shown below, but I also have a different vehicle that has two different valve types on the same system. (Click images to enlarge).
To keep the seals in good condition, it’s always been recommended that the air conditioning is turned on once or twice a month. However, in reality, many people use it in the summer and then again a year later. What some may not realise, is that it’s also very useful for demisting the windows in the winter months, since the air conditioning has a natural drying effect on moisture. (This is possibly also why some people report dry or sore throats after spending periods of time in air conditioned environments).