MG08/15.......value.....
Presently (by your discription...and correct us if we are wrong)....you have a complete MG08/15.
By the discription....we cannot tell if the gun was manufactured in 1917 or (?)....as the serial-number engraved on the top-cover would have to match the serial-numbers on the side-plate.
To better evaluate your gun for value...please let us know:
1: Is it "registered" with the BATF and do you presently have a copy of the registration (?).
2: Is the MG08/15 live or has it been "DEWATed" (?).
3: Do the serial-numbers engraved on the parts of the gun match the serial-number engraved on the side-plate (?).
4: Condition of parts (?).
5: Any "dents" in the water-jacket (?).
6: Any "History" with the gun....such as doccumented capture (?).
MG08/15s are usually priced ("Registered" and in good working condition) in the $6,000 - $8,000 price range if you can find a buyer. But as you said no-internal-parts, no Bipod....correct-?.....I would price the "receiver" at somewhere around $3,000-$3,500 as the missing parts will be hard to locate.
Price for a lesser-condition gun would be lower....and a prime example in original condition/matching-numbers slightly more.
If the gun is not "registered"......you could remove the side-plate (destroy it)...and a complete MG08/15 "Parts-Kit" should sell in the area of $1,500 if everything is in good condition. ....but as you said the internal-parts are also missing......you may only have a water-jacket, top-cover, butt-stock, and a few other parts making it worth a couple hundred dollars if you can find a buyer....and depending on condition.
Some of the harder parts to replace are "working-parts" and the Water-Fill-Cover w/fittings (......but I believe that these and bipods are made as "repos").
One place/"Board" that you may want to ask is over on the WW2-Reenactors-Board....down in the "WWI-Section"....those guys may want it for parts....or to build a gun up from parts that they have....or even to make up a "Gas"/"Propane-Gun" for reenacting.
Again....if we could see what you have...we could price it better for you.
Regards, RichardS in MI.
Blanksguy2001@chartermi.net