good way to check is the track condition, if its still stock, also check all the rod ends for play, check to see how much the skis are worn check bearings that are harde rto change like jackshaft.
sometimes sleds look like they have high milage cause the where not taken care of, or the where traillered with out a salt sheild or cover or if they are stored outside, it only takes one summer to rust the crap out of a sled if its not properly stored.
but yes it would be very easy to change the speedo