I have for the last ten years only used Gardiner poles. SLX's and Extremes.
Alex has been very helpful and his advice to me to get the most use out of a pole has been excellent.
So this is what I do. (I use an Extreme 20 for everyday work - essentially this is the top four sections of an Extreme 25 - almost as light as an Extreme 18 but a little more reach.)
Maintenance. Clean it regularly. Use a towel to wipe the pole hose when putting it away between jobs.
For me at about one year in on my "regular" pole, buy new clamps.
At two years I bought the top three sections of an Extreme 25 (so keeping the fourth section - the fifth is not used as I just pull out my Extreme 47 for higher jobs) which has essentially renewed the pole for just over half the cost of an Extreme 25)
I am a year into this and will shortly order a new set of clamps.
BTW - the three sections of extreme I replaced last year went into my 8 year old Extreme 47, replacing its top three (stepped - and one broken) sections.
A note on Extremes - they are much more fragile than SLX's. Don't close stiff windows with them or drop them!