Change coolant from the green to the extended...

Caterpillar dealers have it for $20/gal. I, being a long haul owner operator would flush it with distilled water to be sure it's clean. CAT extended is pink and lasts a long time, needs to be tested at 300K I think.

WOULD LOVE TO HELP YOU FIND A PLACE
and there is a great place here in Syracuse, NY but I have no idea where you are

Iirc, I paid $20-25 per gallon for the final charge concentrate. Pre-mixed is quite a bit cheaper, but all the recommendations I saw suggested the concentrate and distilled water for mine.

Edit: just found the receipt: $25.99/gal at O'Reilly.

I took mine to a local Cummins Coach Care shop and had them do a drain, flush and refill with Fleetguard ES Compleat OAT coolant, similar to Final Charge.

If you elect to DIY, it is not difficult but time consuming to do it right. You need to know the total coolant capacity of your coach and not just the capacity of the engine and radiator. You will need a lot of distilled water for your final flush before you start adding new coolant.

Be very very careful to only use a Cummins certified product. Otherwise besides a gunky mess you could end up with an expensive engine repair job.

I have been told that it has lasted the three years and should be flushed if I change it, or just drain and put same type back into RV. Same stuff requires the monitoring of SILICA I believe its called and I would rather go with what I perceive as being better. If I get most of it out draining and the filling with water and then draining again, won't it be ok to then put the new type coolant in?

If the procedure isn't done completely and perfectly, you can end up with an expensive gunky mess.
If you've got the green then I would stick with it as it will serve you just as well.