The frame number on the steering tube has been removed by German TUEV and replaced with a "TP-8" number for technical inspection to get it on the street in Germany.
This was a common method in the 70s and 80s in Germany if you did not get the bike from the official distributor or if there were records available to get it street legal.
In Germany no vin plate on a Seeley says "Seeley" as manufacturer,......on every Seeley vin plate is the name of the owner as manufacturer.
Offical distributor for Seeley frames in Germany was Gundolf Birke from Hannover,.....see the guy in the scan.
These bikes have had the SH-GER.... number.
This bike came from the Netherlands to Germany in 1980. Titled and licenced in the Netherlands on August 1976.
Battery bracket and swingarm shows "51 S",...so it should be a race frame,, i guess....no center stand bracket and no oil tank brackets.
So the frame number should be "551",......the number should match the licence date and it should be one of the last "K" series frames. Under the TP number you can see small fragments of the "S" for SH which every frame number started with.
But so far no luck to find out the complete history of the frame by previous owners. And it does not really matter to me. But for sure,.....it's a Seeley.
Last pic shows the condition of the frame when i have received it.
...and yes, it's a Japauto cylinder.