mansfeld was a Polish luthier/small manufacturer based in Nowy Targ if i remeber correctly, quite popular in 80's when getting any decent instrument from the shop was tricky.
In 80's they were made to order instruments but I'm not convinced if they were really good quality build. They were to expensive for me at the time, so never owned or played one.
The serial number starts with 93, so maybe that's instrument from 1993, and it's just cheap production bass. Don't think so it's a rare instrument, maybe in UK
They still making guitars and basses under brand mensinger and marathone.
Hope that help