that what idid as well ,high temp gasket sealer on carb and anywhere else that it could leak.
check ur crank again i thought mine was o.k. too but after inspecting it very carefully i saw the bend not much but enough too damage bearing. [cenracer1 remembers a post some time ago from cen about this]
i think that back and forth play is o.k [ i have that aswell the flywheel can move back or firth around 2mm] because it is the bearing that seals it not the fact that the flywheel is tight against the engine case/front bearing , so unless cen or anyone else who knows different [if they do they might respond] i presume i have the righjt idea.
and u say it wont start, the bearing must be very bad , try getting a new fr bearing should'nt cost much, but as cenracer1 pointed out to me ,if ur crank is bent then u'll be faceing same problem again down the road. have agood look at the crank while rotating the engine [slowly] ,place it on a bench while doing this see if the end of crank is moving up or down ,use the table as a line of sight if u get what i mean , if its a high mileage engine maybe its just simply time for rebuilding ur engine.