The valve adjustment sounds good. Leave it.
The carbs sound a bit lean - maybe try 1/2 turn clockwise first, and have you set the balance at all between them? Off idle response requres good balance between the carbs. At full throttle it matters a lot less, if at all really. The oil in the damper has nothing to do with the return to idle. On Volvo's that is normally a sluggish centrifugal advance mechanism or a leaky manifold to cylinder head gasket.
ATF, contrary to popular opinion, has a relatively low detergent rating. That's why you see all of the fine bits and particles in the pan. They are supposed to drop out of suspension as part of the self filtering aspect of the trans. That last thing you want in a hydraulic system is to suspend contaminents in the oil. Just change the oil and filter at shortened intervals for a while and be done with it.
The front crankshaft seal is about a 15 minute job - if it is still felt, just put another one in there. Be sure to correct any crankcase ventilation problems before you go at any seals. Even a good seal won't hold against crankcase pressure if the breather is plugged.