Steve
I was a really big LGB collector until my neithbor here on the Jersey shore got me into live steam, so of course the first live steam engine I thougth of was the Aster/LGB Frank S. I already had plenty of LGB european passenger cars to go with it. As far as I know they only produced one batch in 1989 of 3,028 engines. So the engines even if NIB are almost 20 years old at this point. So I searched on ebay and within a few weeks had purchased two NIB.
The first one I purchased for around $1,300 was NIB, but the wheels wouldn't turn they were totally lock up. The second one I purchased on ebay was a "Buy it now" for $1,500, but again new in the box. When I received it everything was free turning so I filled it with distilled water and steam oil, lubed all the connecting rods and filled it with butane. The engine fired up on the first try and ran like a swiss watch, it's quite a great little engine and a perfect choice for your first.
The first engine my neithbor Dan helped me with, we disconnected the piston and had to remove the cylinder caps and inside everything was gummed up with a blackish like substance. It was probably some type of lubricate that had dried up over 20 years. After Dan spayed WD40 or some other lubricate like it and worked the piston back and forth it loosened up. After freeing up both pistons Dan then worked on the values for me. Today both engines run perfect and I couldn't tell you which one was originally frozen up. I just had one at the Scanton Pa train show running on the small layout and it ran for 30 minutes or more. If you want it to move fast just turn up the fire and watch the little engine move.
If the engine you are looking at turns freely you are probably all right, even the one I had to free up runs perfect today. They are very hardy little engines. If you run them fast as I do you need to tighten the screws and bolts as I have had some come out on my neithbors raised track, so I have started to use lock-tight on them.
Hope this helps and good luck.
George