What types of dewars does this fit? Is it made by Taylor Wharton or someone else? If it's TW, do you have the glass/plastic tubes? Was it made for use with a 25LD, 35LD, etc.?
As with all things cryo related, they're generally much less expensive than retail. For example, I think Taylor Warton sells their WD device for $800 or something but it sells on the second hand market much closer to $150, sometimes less.
The relief valve getting stuck is a very common issue on these. It can usually be replaced and will fix the issue.