Not sure how this forum is about posting links to other forums but if you want to do an online search there are several threads elsewhere regarding this where Alde have contributed giving advice on which grade of replacement fluid to use. Apparently there is now a 5 year fluid which can tolerate being mixed with the older 2 year stuff, that info came from Alde. Seems quite a few folk on that forum have done the job themselves at around a cost of £50, so quite a saving. Incidentally your local dealership's price to change fluid isn't so bad, mine is just over the £200. Have a look online, perhaps at a place where people talk about caravans? 😗