Any question answered...

Will Sram mtb shifter and mtb derailleur, with Shimano road cassette work? (All 10 speed)

Yep.

Thanks

Sometimes twitter says I am not authorised to view a tweet. Why?

If you can't see it when you're logged in but can see it when you're logged out, the user has blocked you. If you can't see it when you're logged out either, their tweets are protected and only visible to followers, who have to be approved by the user.

Or it's the weird thing that occasionally happens to me when I hit twitter links from here, and it works after refreshing. Not noticed it happening as much recently though.

this, i think. happened earlier on a link from here

Where in south London can I get mudguard eyelets brazed onto frame and a cheap / decent power coat done in the same place?

The Vaz brothers

Ultegra 6700 rear shifter starting to miss or fluff shifts, getting on a bit now and probably rather worn. I have a spare set of newish 105 (5700) shifters — has anyone successfully transplanted the 105 internals into the Ultegra body?

Try a new chain first.

How do I find out who made this, or what app/software was used?

https://www.facebook.com/CurzonArtificialEye/videos/818746801646293/

i'd check chain wear before following @pifko's suggestion

or check hanger alignment

both more likely to be the cause than the internals of the shifter

there's a link in the footer of the movie website to these guys...

http://powster.com/

would be nigh on impossible to know what software they used from a video file though

Did you replace the cable/trimmed housing?

Not uncommon for the cable to get frayed inside the Shimano shifters.

Chain is new

Chain is new and out-of-alignment hanger was checked and corrected

Cabling is new and runs cleanly

You best get a new bike then

Prompt the next question; have you bedded the cables in?

Fatuous

Just the chain? And not the cassette?

Yes, cables bedded in. All is as it should be except that the oldish rear mech lever is missing more downshifts than it should (yes this is a well-known Shimano quirk) and is lazy on some upshifts. I thought this suggestive of a worn ratchet, hence the question, can the internals from the 105 be swapped in?

I don't know for certain, but Shimano shifters don't tend to be serviceable to any great extent.

Either way, wouldn't it be easier just to swap the shifters out?

Does look that way. Thanks for the suggestions, gents.

Lighten up. If you want serious suggestions, you’re on the wrong forum.