I have this weapon, Ser # 3664. Bolt assembly, rear sight and barrel bands do not match ser #, but are correct, I believe. Bore is full of cosmoline. Exterior bluing on barrel is 90%+, with some very slight surface rust in a few spots. Light pitting and surface rust on exterior of receiver. Follower has been ground to permit bolt closing on empty magazine. Walnut stock is dinged up and dirty but still shows some serious fiddleback and strong grain. Absolutely fine two stage trigger. I have not disassembled it yet.
My questions:
1. What am dealing with?
2. Any peculiarities of note with this model?
3. Any particular weaknesses?
4. What is the likely chambering (Of course, I will cerosafe the chamber and take measurements, check headspace, etc.)?
5. What is a likely value range?
6. What do you recommend to clean the wood stock?
Thanks for your help.

Photos would be very helpful. Description of proof marks and such very important. Suggest you start your research with either 'Mauser Military Rifles of the World' by Ball or Ludwig Olson's 'Mauser Bolt Rifles'.

'Cleaning' is fine, but don't 'improve' things. Remove the gunk and dried grease. Do not sand or otherwise alter anything. Simply cleaning the bore and all the dried grease/dust crud will be a step in the right direction.

Value can vary and you need to establish a lot of things. Is it a recent import or a vet bring-back? Is it all original military, no 'duffle cut'? Over the years did it make it's way through different countries military orgainazations (like Turkey)? Value could be a $125 or $1250 depending on all these things and more.

Photos, small details, and research are key.

If the barrel is original, for sure it is an 8X57. Need pictures but it sure sounds like a Gewehr 98, should have a 30 inch barrel. Duffle bag cuts are no problem for me as they show that it was brought back by a GI, rather than imported later commercially. If it is a turkish re-work, value goes down a lot. Clean it with 409 or something not too drastic. DO not sand it or use oven cleaner; that does work but removes all original finish. Send a picture.

Pre WWI Mausers are definitely worth a bit more than 1917 or 1918 mausers, but condition and originality are big factors.

Erfurt made a lot of Kar 98a small ring 98 short rifles and also Gew 98 standard large ring rifles. IUf it is a Kar 98 on the left rail it should have a flattened underneath and checkered bolt knob.

I have it's brother, serial number 4202.