The first step in fix or replacement is to determine if the old system is functionally obsolete - has the need or the application changed so that the old can’t perform fast enough or economically enough?
If so, replacement is probably necessary.
If not, you would want to subject the old (fixed up) and replacement new to a comparison of all costs of owning and operating both over the expected life span of the equipment.
In this case, cost is defined as economic cost which equals accounting cost plus opportunity cost.
Consider anything new you’d want in a fix-up like reduced cycle times, more
marketing capabilities, dryer efficiency, VFD, reclaim, new pumps, tire shine, more bay lighting and signage, paneling, etc. and then determine its cost as well as the cost of replacement new.
Next, determine how the old fixed up and the new would lead to an increase of volume or revenue, an improvement in the image of the business or provide a meaningful cost savings.
Compare benefit and cost for fixing old up and replacement new.
Generally speaking, the alternative with the highest annualized benefit, lowest annualized cost will be the better choice.