Hayward Heat Pro repeated coil failures

[okeesignguy]

When we installed our 5000 gallon in ground pool about ten or so years ago we installed a Hayward HP21002 heat pump to the tune of about $3500...
It worked just fine however after about five years the coil eroded away and disintegrated so we replaced it at the cost of aprox. $3200...
Well now about another 5 years later it has done the same thing and I do not want to spend that kind of money again, heck...that's $6000-$7000 for ten years...that's way too much...

This time I did a little research and found that I can buy just the coil for $600 - $700...

Problem is that I don't know where which online vendors are good and which are not... I would post some pix here but apparently I do not have permission to do that probably because I am a newbie here...

Is that the life expectancy of these coils...? Doesn't seem very long to me for the kind of money they cost...

Any info and/or advise would be very appreciated...