Oh... I think you can post links to them. I'll go see if I can find them.
EDIT:
If it's this one:
https://www.rcnitrotalk.com/gallery/showphoto.php?photo=10544
Then that's an OS 21 RG-X (P):
http://www.southeastrc.com/Items/StdItemView.aspx?lookup=OSM13612, Not a 21 MG...
Sold for around $140 new, but I believe it's discontinued now. Piston/sleeve sets ran around $50-$60 if I remember correctly. Personally, I wouldn't spend that on it. Good solid engine, but not worth a new piston/sleeve to me. It is a great candidate for a re-pinch though, typically $25 shipped. I've owned two of those engines and have seen 4 run.
The two my buddy had grenaded on him (con-rod shattered under 1 gallon of use), so he went another route for his third... then got fired and we lost touch (few years back).
Out of the two I had, one snapped a crankshaft around 8 gallons. The other busted a ball bearing (actual ball busted in half) around gallon 4 and destroyed the engine (ruined the con-rod, sleeve, piston and crank case). The one that snapped the crank got a new crank (thanks to my buddies two broken engines... he gave me all the reminants) and I ran an additional 4 gallons through it. Had it pinched by OS Rocket (too tight), then ran another gallon through it and replaced the bearings (again with my buddies parts). I have run a few more gallons through it since then (2+ years) and it's now my winter aftershock engine. Not a lot of power (even when new), but reliable tune.
That engine was a staple for bashers and racers alike many years ago in 1/8 buggies due to the good low end torque and solid tuning ability. The 4 I've seen/ran will run all day without touching a needle. They all liked to run around 215-250F. Much hotter or cooler and they'd dog on you. We ran them mostly in MT's (21 maxx's, savage, revo, aftershock). I ran one of mine in a buggy for a while. It was a good fit for that. Plenty of power. For the MT's, (except the revo), it's kind of weak in the power department. In the revo (3.3 chassis/new era BB conversion), it was wheelie city.
