I bought one of those 8mm Turkish Mausers from J&G guns in AZ back in '98 while I was in college. :thumbup: It was my first rifle. I think it was only about $40, but maybe $50 because I hand-selected mine from all they had in stock at the time in order to get a nicer one. I spent a LOT of time out in the desert shooting them with my buddies (myself and about 7 of my friends all bought one), especially when a case of ammo (1,000 rounds) was only $70 at J&G at the time. Some of the ammo was even jacketed with a soft iron-based alloy that's magnetic, instead of the standard copper alloy, that definitely penetrated better to boot. I still have a case and a half left.
Mine is amazingly accurate! Iron sights out to 300 yards is no problem!

150 yards or less is no sweat. Such a long sight radius certainly helps.
Anyway, like yours, mine was covered in Cosmoline and required some hefty elbow grease to clean it up. I completely tore mine apart, and cleaned up all the various metal parts in the parts cleaner at our auto shop at school. The stock was a little bit harder to clean up though. In order to re-finish the stock, first I had to get all of the Cosmoline out. On the advice of an old gunsmith who lived next door to my apartment, I built a hotbox to "bake" it in. Nothing more than a couple cardboard boxes taped together and lined with black trash bags. Then I set it out in the summer AZ sun and let it get hot, wiping anything off that sweated out every hour or so. After about 3 days, the wood was bone-dry. :thumbup:
I did a bit of sanding, and then finished with a bunch of thin coats of
Birchwood Casey Tru-oil (a mixture of Tung Oil and Linseed Oil), which I recommend. You can even get the stuff at your local Wally World. I lightly sanded with #0000 steel wool in between coats, but you have to make sure it's dry before sanding otherwise you'll end up with a real mess (ask me how I know...

). Just be sure to take your time. One coat a day is a good call to get an excellent finish once complete. I'd recommend at least 5 thin coats, 7-10 are better.
The final product turned out great, and also I re-finished a Yugo SKS in the exact same fashion in '05 when I lived in TX that also turned out great. HTH. :thumbup: