When the cost of repairs in a years time is more more than the cost of a new unit replacement is a good option.We have some here that think a trans job is cheaper than a new lift so they put a trans in a 10 to 20 year old lift.Maybe the engine hangs in long enough to relize the cost of repair.It mostly a budget thing if is in budget, replace worn problem lifts.If its not repair and pray.Hose,brakes, and mast repairs also add up quick.
A good service tech should be able to give a report of which trucks need replaced and which are solid enough to last