Thats a tough service. Not only is the process fluid awfuly light, but the elastomer compatibility is tough too.
The seal you have is a step in the right direction, the problem is that the fluid is also a terrible lubricator. There are some new materials available that might work well; a graphite loaded carbon or silicon carbide.
Most of the SIHI pumps that I've run into don't have much room behind the pump, but if there is some space consider a Flush Plan 21 (from discharge- to a heat exchanger- to the seal chamber) to cool and pressurize the seal chamber. Consider insluting the body of the pump too, that service is always worse during the hot summer months.
If emissions are your goal, a tandem or double seal might be worth considering too. Though the only buffer fluid I'm aware of that is compatible is very expensive.
I'd show your sales person a failed seal and run these ideas by him/her.
