Eugen,
I can see you have the "sickness", congrats.
The pistol is worth exactly what you paid for it!
You proved that already.
Yes it is a Navy proof crown on the breech block - so it is not an Erfurt toggle train- or at least the breech block is not, the rear toggle may be Erfurt as it seems to have an Erfurt proof on it.
The receiver was not a L P08, Erfurt did not make long pistols except in 1914; but they did cut the receivers in 1917-18 with the sight relief. The frame likely was a left over, since it does not have the final firing proof(unless it was removed at re-work).
The front picture of the frame shows the the mark on the trigger guard, it is an Erfurt frame.
That is not a "5(five)" on the right grip, but a Fractur/gothic "S", from a K date Mauser; so it is not original.
There is no reason to assume the striker is Mauser made, it has two sets of numbers and was likely grooved at re-work.