I noticed my '05 S40 started to release a cloud of oil smoke when first starting.  Although total miles on machine are less than 6k, the bike spent a LOT of time sitting during the previous owner's period ownership.  According to the title records, he put on less than 100 miles over 10 years.

I'm fairly well convinced that I'll find one or more cracked valve stem seals when I open up the engine.  These are inexpensive, so I think I'll go ahead and get a set purchased and on their way.  Should I insist on OEM, or are the aftermarket (Blue or Black) ones equal or better?   Is crusty NOS OK, or the fresher the better?
https://i.ebayimg.com/images/g/7cMAAeSwODZppduQ/s-l1600.webp

Blue aftermarket, Viton?   https://www.ebay.com/itm/311630316867
Black aftermarket?    https://www.ebay.com/itm/394153669799

I see from the forum, that the Cam Chain tensioner is something I should check while I am poking around in there.

What else should be on my short list to inspect / test / replace?

Thanks for your suggestions, I find the Search function here to be notably difficult to use.

Check your oil level.

Does your bike still have the stock vacuum operated petcock?