Very nice saws. I have three now, two good runners, third is waiting on me to get new fuel and vent lines. So far for *me* I have only had oiler issues and that stuff is NLA outside of you might luckout and find the oiler diaphragm (if needed), and the quad ring for the manual oiler plunger (if needed) should still be a dealer part they can get. Complete oiler assemblies though I have not found any.
Inside the oilers that had a piece of foam rubber to act as an air vent, I have found they disintegrate and plug stuff up. I have cleaned mine out and just cut new ones from foam scrap. Besides that, rather straightforward and simple saws. Run strong once you got them tuned. The fuel lines and vent line replacement isn't that hard. The fuel line itself is straightfoward, pull a new one through with a wire, pull it out the hole, stick a filter on, drop it back into the tank.
The vent hole has a rubber duckbill and nipple thing on it, (you can scrounge nipples from most any old junk trimmer, along with the duckbills) that pushes in from the inside, and the small couple inch piece of scrap fuel line pushes onto that from the outside, completes the seal. You'll see the two sizes of holes on the fuel tank. The larger on the right, closer to the rear of the saw is the vent, and just tuck the two inch piece down there sorta under the carb, below the kill switch wire, out of the way of the case screw. Anyplace will work as long as it is out of the way. The regular fuel line just goes to the carb on the other side, and you can see a routing space for it on the case there. Easier to put it on with the carb loose, IMO.
Modified Mark has an excellent tutorial with pics on doing that here
http://www.arboristsite.com/chainsaw/85259.htm
Clean the carbs, or do a kit if needed, so far I have only needed cleaning. Aw shoot, see if my memory works.. I *think* those are walbro hd-8s? (someone help if that isn't right) something like that, on the carb. Those kits are universal and readily available and fit tons of carbs.
I see no reason at all the 3400s couldn't be a quite good "one saw plan" for general personal firewood. They rev good, pull in the cut hard, can run a 20 easy. They use a D176 bar mount, still out there in a variety of sizes.
Good luck! Stout, fun saws!