Holy smokes! First off, you'll most likely have a problem getting that LU off, which will most probably require a heat hammer (torch)
. PRAY you don’t break a bolt (or stud) , which I honestly think you will.
As far waterpump service and thermostats, use, salinity, and overall cleanliness (sand, silt, etc.) of the water you run in, and “how” you run it, can affect the longevity of the impeller and t-stats.
That said, a general rule
is to perform the full waterpump (including new impeller, key, wear plates, O-Rings, etc.) and thermostat service every 200-300 hours or every 2-3 seasons. Some do so annually with significant use. Any of these periods above are “cheap” insurance to the long life of the motor.
On my smaller OBs (< V4 powerheads) I may get 6-8 seasons out of the impeller, or more, but you can bet $$ I pull the LU bolts (1 at a time) everey 2-3 seasons - clean them, re-lube them (use gasket sealing compound) and re-torque them. Then at least I have a good chance of removing the LU in the future without breaking a fastener.
Like you, I’ve had impellers last LONG past 10-years, but now that I do my own service, it’s not a big deal … just $45 or so for the kit (not including t-stats) and < 1-hour of my time. A factory OEM Service manual is worth its weight in gold here! It's not too difficult.
So … since you asked … yes, I’d take it in … but be prepared to spend some $$ if that puppy doesn’t want to come apart or it doesn’t come apart easy.
FWIW, for this type of work I know some marinas love it for "winter work", so that it gives them something to carry them through the off-season. But I don't know of any Suzi dealers south of Boston. But note, for this, you don't need a Suzi dealer, Monhahans in Weymouth could do it (tell Wally I sent you), as could 3A Marine.