Detroit 6v92TA
(Low profile's)
Alison Gears
Westerbeke
12.5kw Genset
Given how that couch is laid out and such, I would think you don't have much choice.
My layout had an L couch that was useless and uncomfortable to sit on, that isn't the case with yours. I replaced mine with an after market one with a ton of storage underneath and was a home run. I don't think you would be able to replace what you have with anything new and still have the same look and feel that does. JMO.
I would shop that price around a but more though. Seems a bit high to me.