I had some indirect involvement with the Irish SF260W machines (not recently!). They were very reliable, given that they were used for primary training (pilots trained on the Marchetti and Fouga Magister, then when they got their wings they went onto the Cessna 172).
Only recurrent problem was the 'engine bearer arms' as we called them. The front undercarriage was bolted directly onto the engine cradle rather than directly onto the front bulkhead. And every time we did NDT on the 2 lugs they were cracked. There was an approved procedure to grind out the cracks (to a certain depth), but this was not very successful.
I know there was an AD about cracking at the end of the main wing spars. Both spars were connected together by two cheek plates at the root, and there was an AD (can't remember the exact details) about a repair. Make sure this is done.
There was also another AD about cracking on one of the pivot arms for the undercarriage mechanism (with was an electric motor and a series of rods).
Only other problem (that I can remember) was that under the anti slip coating at the entrance to the cockpit the skin was liable to get some flexing from constant use and this cracked a small stringer underneath (not primary structure). Easily checked by looking up underneath the wheel well.
Most common problems was actually:
1. a live mag due to fracture of the ground wire onto the magneto. Could never understand why they didn't just put a loop on the wire with some extra length and
2. the release for the inertia reel on the safety harness. The wire connecting the lever of the side wall to the reel kept breaking. At one stage I went to a bicycle shop to get a replacement cable.
I know parts were very expensive, and could take a year to get. The air inlet filters were very expensive considering what was in them. We even made replacement elements ourselves from those used on the Cessna engine.
All in all very simple and reliable. But parts were expensive and took a long time to get.