Leak Issue with akvaterm accumulator tank

Evening, hoping someone can help me as I'm looking at a pretty hefty replacement bill if not.
I've a solar system, in approx 7 years. I've a recent issue in that a steady dribble of water is escaping from my tank at the location where the solar pipe runs into the tank. . I say at the location because it's not coming from the joint but rather from further in where the pipe runs into the tank.
On inspection the insulation around this point is brown and dirty and there is a bit of rust there as well (which confounds me as I thought this tank was stainless steel).... The other connections around the tank are also brown and signs of damp.
While I don't expect these tanks to last forever I would have thought that they would last for longer than 7 years and I'd be very hesitant in putting in a new tank unless I found out what went wrong with this tank given that they run circa ,€3500
Other issue in the past is that I've had to replace the element.
Any help would be greatly appreciated.
Thanks
Brian