I owned an Oceanis 400 (94) a few years ago. She was a great sailing boat. I paid $115,000.00 but ended up spending an additional $55,000.00 to get her up to speed. Watch out for the toilets and piping. I had a plumbing nightmare and associated odors. Batteries, Chargers, Air Conditioning Heating unit. Make sure that their is no bad smell that cannot be removed. Beneteau's have small bilges and any septic that creeps into the fiberglass stays there forever. If the boat is not up to date in the electronics department check what it will cost first to get it up to speed. Check the bottom closely for any blisters or peeling.
I apologize for all the negatives but I don't want you to be disappointed by the high cost of repairs.
On the positive side she was a great sailing boat. Probably the best handling boat I ever owned!
The 351 is similiar and was the predecessor to the 361 which we had for 7 years. Nice stable boat for it's size, not the best sailing boat in the fleet but will perform if you keep her trimmed properly. Handles rough seas well. Nice creature comforts below which should keep the Admiral happy. The 351 had the genoa cars on the cabin top and I heard it could make trimming the genny a little more challenging. As for reliability we're on our 4th Benny and have had very good luck with all of them. No major failures with any components. The good thing is Beneteau uses equipment from major manufacturers so your generally have a large source for replacement parts if you do have a problem. They also have a parts section on their website and can provide you with replacements at very good prices. Have a good survey done on her. It will tell you just what condition she's in. Good luck.
We have sailed a 1998 Beneteau 352 for the last two seasons in the Cheaspeake. This is the (nearly identical) successor model to the 351 which you are considering. We are totally satisfied with our boat and looking forward to many more seasons of fun. It is a good sailor, reasonably fast in comparison to other 35 footers, comfortable in harbor, and spacious in the cockpit. Also, maneuvering in reverse to dock stern-to a slip is a snap once you become familiar with the boat.
But be sure to get a survey by a competant marine surveyor, and make arrangements to be present during the survey. You will learn a lot about your boat and the time will be well worth while even if your boat gets a clean survey. If the survey comes back with problems you will be able to protect yourself by either refusing the purchase, or bargaining down the price to reflect the cost of repairing the defects.