Heat Pump Routine Maintenance

We bought this house 2 years ago and we have two 19 year-old Trane heat pumps with gas furnace backup (XL1200 I think). We have not done any routine maintenance in 2 years. Last time we called a pro to take a look at the water leaking in the winter from the backup furnace, he said - system is too old to fix, replace it now or let it run and call me to replace when it dies.
It's been working fine since then (only once not being able to cool the house in the summer when we had people over and lots of cooking was going on). I do however want to prolong its life span by maintaining it. Here are my questions:
1) What is normally included in the routine maintenance done by a pro? What does it normally cost (if no repairs needed)? I do not want to hear another sales pitch for a $12,000-dollar system if I can maintain this one. I also do not want to pay for someone to come out, measure CO leakage and charge me $100 for it - I have a CO detector to do this job.
2) Is routine maintenance worth the money or those systems run well without them?
3) Can they check if freon refill is needed at this time of the year (November in PA)?
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