thetypewriterman wrote:

Yes the centre guide is 'the fork thingy that the type-slug has to slot into before smacking the paper'   If adjusting 'the fork thingy' cleans up the alignment but you still have a few sticking typebars, you may have to form (bend) them to suit.  The typebars are quite soft on this model so less danger of breaking them as on other makes. If you need to form the typebars let me know and I'll do another post to give you some idea of how to go about it.

I think a description of how to form the typebars would be most welcome in any event! I know I've got one machine that needs a little bit of this, but I'm terrified of messing it up.

thetypewriterman wrote:

Yes the centre guide is 'the fork thingy that the type-slug has to slot into before smacking the paper'   If adjusting 'the fork thingy' cleans up the alignment but you still have a few sticking typebars, you may have to form (bend) them to suit.  The typebars are quite soft on this model so less danger of breaking them as on other makes. If you need to form the typebars let me know and I'll do another post to give you some idea of how to go about it.

Haha, thank you for confirming that
This afternoon I fiddled some more with the Sterling and I'm back to report on the state of things. I reslackened the screws of the centre guide and adjusted the p and q, like you suggested. I hadn't realised how much leeway there is for positioning that piece (and so many ways to get it wrong too). Here is my best effort:

I can't believe I typed this on the same machine. Needles to say, I'm very pleased with this result, even if though I'm back to having a few sticky keys.

Typewriterman, many thanks for offering your advice, I'd be happy to learn how to form typebars in a civilised manner.

That's a very impressive improvement !  Well done !  Now to forming any sticking typebars.  Press down and hold the spacebar and with the other hand try each character in turn.  In theory, each typebar should drop back under its own weight.  I'm sure that you will find that a lot of them don't.  Remove the ribbon and poke a piece of white paper behind the centre guide.  Find a strong desk lamp and position it so that the centre guide is illuminated.  Now try the first sticking typebar.  Observe closely and you will see that it is rubbing on one side of the centre guide - this is what is holding it up and not allowing it to drop back.  What you now need to do is form the typebar so that when it comes up it will go into the middle, not to one side.  With the soft typebars on your machine - no tools required - just your fingers !   You use your thumb, index finger and middle finger.  Let's say you want to form the 'H' typebar to the left because it is rubbing the right side of the centre guide.  Place your thumb near the middle of the typebar (left side) with the other two fingers on the right hand face of the typebar spead each side of your thumb.  Apply pressure with your thumb and you will see the type bar begin to bend.  It takes years of practice to do this accurately, but apply a little pressure at first, and try the typebar in the guide.  If it is still rubbing in the same place, try again, a little harder - and so on.  Go too far and you might have to form it back the other way.  Do not apply too much pressure - you could break the typebar !  Alway apply pressure ABOVE any area that works in the segment slot.  Bend that area and you will have to remove the typebar and hammer it flat !  I don't think that you would want to have to do that !  Go carefully and I think that you will get the hang of it.  You have an ideal 'typebar forming beginners' machine there because the typebars are relatively soft.  This is a double-edged sword in typewriter design because that very softness is how the typebars got distorted in the first place !  Good Luck

That is amazing, and I'm happy you did not waste too much time on the other idea and listened to expert advice instead! It makes me want to loosen that type guide thingie fork slot... thing... and experiment with reproducing this effect.

This reinforces another observation ... that if I neglect the nagging internal voice which asks me to write in some cautious logical qualifications and plow right ahead I will be completely wrong 100% of the time! At least it seems that way to me.  I did repress one doubt which I should have heeded... Mr. Doubt, sir ... that the steady trend in height had a non-zero second derivative whereas if it were due to a tilted basket or carriage I might have expected it to be linear.  Ooh... I remember derivative thingies.