After 1.d4 d5 2.e4 dxe4 3.Nc3 Nf6 4.f3 exf3 5.Nxf3 c6 6.Bc4 Bf5 7.Bg5 e6 8.Nh4 Bg6 9.Nxg6 hxg6 10.Qd3 Be7 11.0-0-0 Ng4, black seems to be clearly on top.
Not that this is the only problem to be fixed - after 11.0-0-0, a quick scan with Stockfish unearths many more problematic black moves, but that is another problem...
Back to the lines aftre 11...Ng4. It is obvious that 12.Bxe7 Qxe7 are necessary.
In my previous post, I only considered the aggressive 13.Bxe6, but now I am pretty sure that 13.Qf3 (diagram) is the best move.
It seems to me that both 13...Nf6 and 13...Qh4 are possible for black. Let;s look at 13...Nf6. White now tries to open the centre with 14.d5 (diagram).
It seems to me white has at leats an equal game in all lines, apart from one : 14...Rh4 !!! (diagram) Obviously, this move is hard to find over the board, but it poses white some serious problems.
a/ 15.d6 Qd8 16.Qe2
...a1/ 16...Nbd7 17.Kb1 (=) to (=+)
...a2/ 16...b5 17.Bxe6 fxe6 18.Qxe6+ Kf8 19.g3 (=)
...a3/ 16...Kf8 17.g3 (=)
...b1/ 15...cxd5 16.Rhe1 (=+)
...b2/ 15...Nxd5 16.Nxd5 cxd5 17.Rhe1 (=+)
d/ 15.dxc6 Nxc6 16.Bb5 Qc7 (=+)
So we see that 13.Qf3 Nf6 14.d5 Rh4 15.d6 Qd8 16.Qe2 gives a hard, but playable game.
What a relief, I beleived for some time the Ziegler actually did refute the Blackmar Diemer ! but that does not seem to be the case - provided I can fix all other problems :-(