Actually VM has used proprietary 38" membranes in some of their units. This was not an uncommon practice when watermakers first became popular for smaller boats. But if you are fairly handy you can easily replace your existing membrane vessel for a standard 40" vessel that fits a SW2540 membrane. It's a fairly simple plumbing
job. But if you buy a new membrane vessel along with some plumbing parts
and the $200 membrane you found your intial costs will still be around $500-$600. But if you will be using this watermaker
for several years it might be worth the cost if you go through several membranes in the future.