Patrick, I bought my M41 in 2000 and am delighted with it. The survey should give you a good guide to where to start looking. The following is from my own experience.
1. Keel bolts. These may look rusty also the bottom of the mast compression post but a good wire brushing revealed nothing too bad. I have used Hammerite on them.
2. Fuel tank is made of mild steel. I replaced mine several years ago with plastic. At the same time moved the filler from the corner of the cockpit sole (disastrous position) to just inside cockpit locker – excellent. If you contact Tek-Tanks be aware of my repositioning of the filler and that I should have positioned it slightly further forward.
3. Water tanks. Leaking from the top when tanks are full especially as the lower tank gets pressurised from the up hill tank when heeled. Also had some osmosis as the tanks are fibreglass. I installed two taps in the cross-flow pipe so that I could select from which tank I was using water.
4. Saloon windows with small leaks – windows re-bedded.
5. Chain plates. Check condition of the sealant around these on deck. I have periodically renewed my sealant. Access to the underside of the chain plates is not easy and requires making some access ports.
6. Look for any slight lifting of the deck especially near any through deck fittings. This could indicate water penetrating via the fitting and getting into the wood core between the two layers of fibreglass. Easy to repair but takes time.
7. If it has the original Thornycroft engine then it is possibly nearing the end of its useful life – I have replaced with a Beta 60 with which I am very happy. But be aware that any engine change could require reviewing the propeller.
For more details your friend really needs to join MOA as there is so much advice in the Information Exchange, the Technical library, articles in Compass magazine and in the archives. I have done various small changes to my M41 – generally improving access with improved stowage, companionway steps, ventilation to bunk cabin, cockpit locker hatch, anchor bow roller, etc.
If your friend is looking at the M41 that I know of in Kent then I know the previous owner and he appeared to be very thorough.