I finally managed to get hold of a hen's tooth in the form of a Vivitar f2.8 55mm 1:1 macro lens.
Here are a few initial shots with it on a K3-ii. A lot to learn yet but its reputation is certainly upheld so far......

It's sharp wide open - you just don't get much DoF. only one edge of this dhalia is in focus. The rendering is rich and vibrant
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Stopped down it makes a very good job of things
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Bees are hard to focus on generally but this bokeh is wonderful !
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Taken with the same lens, this is just to show what the actual plant looks like. It's a common saxifrage.
In common with most macro lenses it does non-macro well too.
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Three of a single saxifrage flower with varied lighting. You'd never think that plant was so pretty !
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The only downside is just six blades, which gives a slightly harsh, hexagonal OOF 'circle'

And some more of that lovely bokeh
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With some closer detail
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I'm getting slightly worried that my other macro lenses are going to be made redundant.
Your comments are welcome.

I like 6 for its pure simplicity (but all of them are first rate)

Like the Jags, there must be a bob or two in spare parts there.

The ads that annoy me (and are a good advert for Pentax) are those that go ... "Pentax lens. Perfect for Canon Nikon".

K5 is a lovely camera but if you can afford it a K3-ii is even better. Since you had a Spotmatic you know all about M42 lenses. They're cheap as chips now and they marry up perfectly with a K5 but do spend a few bob on a Genuine adapter for them (some of the cheapos get stuck in the camera !).

That particular rear converter doesn't cost the normal arm and a leg. You see them on E Bay for £40 - 50 and, as you can see, they deliver. (I paid £5 for mine).
Another fairly good one is the K T6 - 2X which does not have the through-contacts. Wish I could get a 300* at bargain basement price though

The yellow is easy to shift. Take the front cap off, wrap it in kitchen foil shiny side to the body, leave the yellow rear element exposed to daylight and put it on a sunny windowsill for two weeks. The UV reverses the yellowing effect from the radio-active thorium in the rear element. The foil reflects it straight back out so the lens gets two doses of it.
Here is mine cooking away. It's crystal clear now.

Have a look on Ebay. Most of the CDs come up for sale sooner or later.
Have you tried Nikonview? (washes mouth out). I used to use it in preference to the Pentax offering.

No 2 really makes you sit up and take notice - well seen.

It is indeed a splendid walk and you've done it proud here. But if anyone is thinking to follow this example, be warned, the climbs and descents along the cliffs are formidable! The photo shows the initial ascent onto the army range ..... and the one in the background is even worse!