Hi Sepp-
Mentor is a company that was around at that time, so it's highly possible that they contracted with Germany for watches. Its not a very well known brand and it would be interesting to see. I can't seem to find much info about them.
The movement
should be an AS1130 (Anton Schild 1130; AS is a manufacturer of watch movements) and may be stamped 'AS1130' on the bridge plate. But if it's not, no big deal. Some companies used their own mvmts. Please post some pics (dial, back, movement).
Don't worry about the strap. There are lifetime collectors that have yet to see an original strap, so a well made replacement in the same style is totally acceptable.
It sounds very likely that, if legit, it could be a very early issue watch. The serial numbers for standard 'field' watches went into the 6 figures towards the end of the war (500k+), and yours has a 4 digit number.
Also of interest is that German made watches will not have a D/DH/DU coding. That coding was used only by the Swiss manufacturers, so German manufactured brands like Stowa, Laco, Wempe, etc. do not have this designation in the serial number.
Another tidbit; the rarer D-U designated watches had no serial number at all. There is no surviving paperwork to support this, but the collector thinking is that these were watches that were given to civilian support and political personnel, most likely pre-war since the cases were typically stainless of higher quality than the standard soldier issued field watch.
-Kevin
