I just did impeller in the fall in my b2, old one looked almost perfect. First change in 2 years I've had boat, and previous original owner didn't remeber ever changing it, but may have been done with bellows 2 years before I bought. I am only boating in fresh water, but sometimes very shallow sand. Oil (both engine and outdrive) done in fall every year.
1997 1700SR "MaKs RAT attack"