Here is the page from the on-line Honda GXV140 service manual, showing specified torques for the most important bolts:

[Linked Image]

I think your dealer looked up Honda's standard torque for a 6 mm bolt (7 lb ft unless otherwise specified), rather than looking up the actual bolt.

I don't know where the rumour that the crankcase cover gasket is unavailable, came from. The part number is 11381-ZG9-T00. Here is a US dealer listing for it:
http://www.2lcstore.com/catalog/item/4771015/4843300.htm

The crankcase cover, and the gasket, are the same as for the Honda GXV120 engine, which is still in production, so it would be unlikely that the gasket would be discontinued. I suspect whoever told you the part was not available was looking it up in the wrong way. The GXV140 engine went out of production in 2003, so some of the parts listings for it may be getting a bit erratic by now, but the majority of the parts are the same as GXV120 ones.

Never substitute sealant for a gasket on a small engine's crankcase cover. On Honda and Briggs engines in particular, the thickness of that gasket controls the end-float (i.e., axial slack) of the crankshaft. The sealant has a compressed thickness of almost zero, versus about 1 mm for the gasket, so you would be reducing the end float by 1 mm. I don't know of a specification for the end float of the GXV140 engine, but for the GCV160 it is 0.1 mm to 1.0 mm. Unless your engine is fairly worn, it might have negative end float without the gasket, which would cause it to lock up and refuse to rotate when you tightened up the 7 crankcase bolts. Some engines (in particular, Honda's OHC mower engines, which are for "residential use", compared with the OHV engines like yours being for "commercial use") originally use sealant instead of gaskets, and of course the crankshaft end float is designed accordingly. You should always use the parts specified in the original design, unless you are planning to experiment with a modified engine design for some reason.

When a gasket has leaked, it is good practice to replace it. In this case, when you have the engine out of the mower and can replace the gasket with very little work, it would be best to do so. However if your local dealer can't supply the part, it may take you a week or two to get one from the US (Canadian customs delays are somewhat notorious, though Australian ones are much the same) and I suggest you don't remove the crankcase cover until you have the gasket in hand. Gaskets fairly often break when the parts are dismantled. Remember when you talk to your Honda agent, the gasket is the same part as the GXV120 one. If he cannot supply GXV120 parts (possibly Honda's most popular engine, ever since it was introduced in 1983), I suggest you choose a different agent in future. Frankly, he doesn't seem to have covered himself in glory with this repair process.