This log splitter gets about 15 hours of use every fall and spring and hadn't had any maintenance since August of 2012. We're looking at a lot of dead trees right now (Emerald Ash Borer).
I bought a 2 gallon container of ISO 46 hydraulic oil at Rural King and a NAPA filter at the dealer for about $30.00. Specs are for a Speeco Splitmaster 15 ton. You can read the manual here: http://www.speeco.com/whitepapers/LS401105LOGSPLITTER%20MANUAL2010.pdf
This has been a good splitter and never eaten any hands. It doesn't use a lot of gas and handles every kind of firewood. I also changed the spark plug ($3.00) and the engine oil (Mobil 1 10w30) which were both very burned out/dirty. The listed capacity for this engine is only 0.6 quarts. Swapping these made a noticeable difference and it starts in one pull now.
The oil had obviously sheared (?) quite a bit and had a dark tint, but there wasn't anything alarming in it.
I split the filter open (all damage to the media is mine) and didn't find anything in there either. It obviously wasn't in bypass, but I was concerned about deterioration.
I flushed the breather out and ran the cylinder unloaded a couple times; 2 gallons was about right. I didn't notice any air in the system, but I suppose there could have been.