The 2400 is an 18 inch unit. With the 4 cyl. engine package, well consider it as a heck of a 15 inch unit. Great for handling tops, larger wood, well it'll struggle.
If it's a non XL Version (very likely 97/98 were the break points) it will not have the fan along side the drum. Meaning light leafy material, punky wood, wet pine, etc will cause it to plug up. Only solution to this is only run new blades, those that have been resharpened will not generate enough velocity to push that material out of the chute.
Take a look at the anvil mounting area. Way to many operators never bothered to adjust the anvil after having their knives sharpened. Resulting in a huge increase in impact force, anvil mounts will bend/break (typical with any drum type machine). Has the anvil been flipped (ask the customer, then verify by taking a look. You should be able to see even the back side of the anvil edge that is currently being used. Is it sharp or rounded. If it's rounded, likely they have kept up on flipping/adjusting.
Bearing: Engage the PTO and bring the unit to full throttle. Disengage the PTO and shut off the engine. You'll be able to hear if there is bearing noise, main drum bearings. If they are original likely you'll need to replace $1K. You'll also be able to hear the output bearing on the PTO. Is there slop in the PTO handle (meaning does it bounce around not the normal end play).
While the drum is slowing down, watch for excessive vibration. I normally set my coffee cup on the fender while I'm looking around the unit. Excessive vibration with knock that cup off the fender. This will let you know if the drum is out of balance.
Open the access door to the knives (AFTER THE DRUM HAS COME TO A STOP) and take a look at the knife holders. The middle of the holder will be worn back (where it supports the knives). Take a look at the difference between the sides and middle. Much more than a 1/4" is excessive. Another $1K to replace.
You should be able to fit your hand between the tires and fenders. If your hand will not fit, likely the bushings on the torflex axle are shot. Should also see excessive wear on the tires (like a car that needs an alignment).
Plan on draining the hyd system, flushing and replacing with fresh fluids/filters.
Pull the air filter and look inside the tube, do you see dirt? If so that means your getting dirt inside the engine (doesn't take much more than a couple tea spoons to wipe out an engine).
General check of the infeed (pay attention where it bolts to the drum housing there should be 4-6 bolts (depending on year) on each side. Are they there? Does it appear it's been patched? Later units had a frame extension added that supports the weight of the infeed, instead of being held in place by those bolts only. Units that were machine loaded or seen very heavy use or worse driving on nasty roads at high speeds, were subject to cracking in this area. Not a tough repair, just labor intensive and costly if you can not do it yourself.
After all the above, go run the unit and make an informed decision based on that.
But based on what you are saying, it sounds like you should be looking at a model 15 (2005 plus if possible so you get the reversing auto feed, electronic auto feed system, Hyd. down pressure, etc). 130/140 HP with a winch. Price range for such a unit in good condition ~$25K.
Good luck and let me know if you have any questions.
