Strictly by the lack of proofhouse proofmarks, I don't see any; therefore, it would be a pre-1893 longarm. So this might be an exception to the serial number list. But it was slated to take a boat ride to a country that didn't have a prooflaw, so it is possible that it was made post 1893 but I would expect to see at least some preliminary proof stamps. Interesting that it has "Thuringia" on the flats, which became a part Germany in 1871.
It's not a sidelock or a boxlock but is something inbetween as the hammer is in the wood while the mainspring is in the bar. The scear and accoutrements, including cocking indicators?, are mounted on the sideplate. The inverted "L" pin configuration is the tell-tale sign. It was a quality piece worthy of being shot today as it has the stamp set of Sauer crowns noting craftsmenship and shoot performance as well as bushed and disk set strikers. Empirically data was acquired thru time and effort being expended in actually patterning the example. I haven't looked closely, but there looks to be a set or 2, 3 or 4 cavemen with a staff(a quality mark???) on the underside of the left tube near the "5301" stamp. I'd probably put it in a steady state now, as per the excellent description above, and use it but there is the option of restoration. Any yes, invest in a good set of turnscrews. RST and Polywad(
http://www.polywad.com ) are sources for 65mm ammo. I checked Mr. Jim Cate's Sauer text and there's a gap in his serial number data from say 53k to 56k in the serial numbers. Mr. Cate of Chattanooga has a very good reference.
Kind Regards,
Raimey
rse