Bavaria did not adopt the Prussian style spike helmet until 1886. The helmet on ebay is essentially a modification of the Model 1868 Raupenhelm. From the photographs, the helmet shows evidence of possible recent alterations.
These style helmets were also worn by Schwere Reiter regiments from about 1879 until 1886. However, the Schwere Reiter helmets usually have the same 2 piece front plate (Crown above the letter L) as used on the Raupenhelm. After 1886 Bavarian helmets in the Prussian style are seen with fluted spikes for certain units. The following Bavarian helmets will be found with fluted spikes, All officer helmets, Schwere Reiter regiments, Cheveauleger regiments, field artillery regiments and train Bataillons. Infantry and foot artillery units wore smooth spikes. Bavarian artillery units did not adopt the kugel (ball top) helmet until 1914.
The following Bavarian units wore helmets with silver fittings: Infantry Leib regiment, 1st Schwere Reiter Regiment, Chevauleger regiments 2, 4, 6, and 8, 2nd Ulan Regiment, Pioneer Bataillons, Eisenahn, Telegraphen, Luftshiffer, and Kraftfahr Bataillons. Helmets for other Bavarian units had brass/gilt fittings.
I hope the above helps.
Reservist1
