My rule for deciding to fix anything is very simple:
If I can fix it (1)myself with (2)readily available parts (local store or online) for (3) less than the cost of a new [insert object here], then proceed.
Otherwise, I initiate replacement discussions with my Wife.
In your position, Techidave, I would advise to not underestimate or overlook costs of downtime
as the machines age, along with your long-term projections of potential repair costs. A few hundred on repairs is not that much if the machines are actually
reliable and repairs are easy, in which case you've got a good argument for repairing vs. new. Just don't ignore how quickly things can add up when repair visits become more frequent over the next 2-5 years, and how much time (money) you'll be losing waiting for repairs to be done as parts become more scarce.
Hopefully you (or somebody responsible) has been keeping reasonably detailed records of repairs, supply usage and costs (newer machines are often more efficient with materials usage), and duration of downtimes so that a solid case can be made to justify either choice.