What comes to mind, and this is without knowing much of the OPs situation with the Jasper engines — usually I’ve seen Jasper as an option offered by shops and sold to customers. Versus your typical Joe Blow going to them, buying their reman engine/trans and then taking it to a shop for installation.Why is it your shop's fault that Jasper has bad quality control?
I am not sure if Jasper even sells to an individual without being an authorized reseller/installer.
If the latter is not the case, where as the shop did the sale of a new engine, etc. there should be a limited warranty that Jasper provides that is what the OP would be getting. In that case it isn’t OP or really the shops fault, but the shop sold the “part” and should make right on it. But three times is a rough go.
Probably a crummy pan on the Jasper engine after reading through all this.
I don’t know if I personally would go with a Jasper reman. I’d probably go with an acceptable mileage (acceptable to my requirements, cost, use) junkyard used motor or take it to a local machine shop for rebuild.