Glad to hear you are enjoying the Sei, mine is working well for me in regular giging band, it's more rock based, but it still does a great job.
The one you have, has a U-retro? Next step for me is a J-retro, just need some adjustments making to the regualr set up to make it work for me (need LED switch)
The 5 string fretless mentioned earlier, is possible Paul Turners old bass, that was made around the same time mine was, they were both made for Mr Turner and are very early jazz models
Cheers
Tony