HI Phil,
Yes, thats a neat cover, it looks original all around, even the attaching nooks are still present, thats a nice cover in a very nice condition. It seems that even the interior lining of the spike is still lined with leather. Even the cover alone will be pretty expensive. Thats a neat one!
there is a "10C" mark stamped, will try to check out what does it mean.
The rgt 153 is the
8th Thuringian Inf Rgt No 153, does the cover comes with the helmet? I can see what looks like a M15 haube under the cover

Wow, You have another haube? Pls post them again.
The red numerals were used prior to the great war and soon fter the war broke out, the green numerals were used instead. The use of these numbers were discontinued in 1916, i guess coz there were too many new/replacement regiments that were raise and it will be a trouble/time consuming in numbering them.And the helmet underneath looks like a M15 haube, whereas the cover is a pre War ones, did they came together? They looks prefectly matched in size.
By the way, you bought the cover 25 years ago?? Thats very impressive! We can lean so much here.
Cheers and good day,
Mush