Hello. Stihl made 2 versions of the S-10. A top-handled version was made from 1968 to 1973, then a rear-handled version was made from 1973 to 1978. The S-10 was originally produced to be Stihl's "consumer" grade saw, but they do seem to hold up rather well. They are almost identical to the Stihl 08 & 08S saws. Most parts are still available through Stihl.
As for a replacement chain, you said that it is a .404" pitch chain. The gauge should be .063". Are there any numbers stamped onto the sides of the bar and on the chain drive links? You will have to count how many drive links are present on your existing chain. (Drive links are the chain links that fit down into the groove on the bar). This will give you the basic information needed to buy a chain that will fit properly. Then there will be several variations in the style, or shape, of the actual cutting links. These are normally selected for the conditions that you will be cutting in, which can be basically broken down into whether you will be cutting clean wood or dirty (abrasive) wood. A chain designed for cutting in clean wood will have the ability to cut faster than one designed for dirty wood. The chain designed for more abrasive conditions has the advantage in that it will hold an edge much longer than the chain designed for faster cutting. .404" chain is not real common as some of the smaller gauge chains, but it is definitely available. There are many places you can buy it from if your dealer does not stock it or is trying to bend you over the counter. A number of ArboristSite sponsors can get you set up. Bailey's is one of the best companies out there to do business with, and there are others who can also get you set up.
I would suggest replacing the drive sprocket on your saw when you replace your chain. This is the gear that pulls the chain around on the bar. They do wear out and are frequently over-looked. A new chain will wear prematurely if run with an old sprocket.
Manuals. You can order an owner's manual from Stihl USA for a 08S for free. This would cover proper operation but not be an IPL.
http://www.dealerlocate.com/StihlUSA.aspx
Fill in the form. There is a selection box at the bottom of the page. Scroll down to
Chainsaw 08S & click on it. Stihl will mail you a copy in about 1 to 2 weeks. (You can go to flea bay & someone will be glad to sell you one if you would prefer to pay for it.
).
As far as getting an IPL (Illustrated Parts List), you will need to post an email address so that someone can send you a copy. Is your saw the top-handle model or the rear-handled one? There is a "sticky" thread at the top of the chainsaw forum titled "The Beg For Manuals Thread" where folks normally would put in a request.
As for the differences between the S-10 top-handle and the 08S, I can only think of a couple. The name on the side of the clutch cover/oil tank is the most obvious. The early S-10 saws had a slightly smaller piston & cylinder (44mm) than do the later saws. These have what appears to be 2, round-shaped plugs glued to the outside portions of the transfer ports, one on each side of the cylinder. The newer saws had either a 47 or 49mm piston & do not have the glued-in plugs. The S-10 did not come with a front handlebar brace (a piece of nylon plastic on the bottom of the handlebar which meshed with the crankcase). The S-10 came with a cast aluminum muffler and the 08/08S came with a sheet metal muffler. The S-10 never came with a bucking spike, but you can easily add one to it if you want.
