I'll probably be at the Clacton Air show both days - entry is free & it's only 10 miles from home, so it's just a case of arranging holidays to fit.
I'd like to attend RIAT &/or The Flying Legends but I'm not sure if family commitments will allow it

It's no 1 for me too.
The second is actually my second choice -even with the grass

Not so much cheap as inexpensive. They're much better quality than the cheap Chinese ones (which screw together). I think my first ever set (brought 20-30 years ago) is identical to these, they still work perfectly too. The only down side is no pass through of electrical signals.

I wish Pentax (& other camera manufacturers) would give some better guidance of weather sealing. An initial IP rating would IMO be ideal, adding a note to say something like 'as lenses are changed etc the seals may degrade so this rating may not last' would I think cover them if an older camera failed under less severe conditions

I must say I've always been impressed with the degree of sealing of my K7, though as most of my lenses are not weather sealed I tend not to use it in poor weather much.

I suspect just refitting the adapter part properly will solve it. I find they can be a bit fiddly so are easy to install wrong.
If the mount adapter is faulty fairly unlikely PK versions are quite cheap, I think I've seen loads at ~£5.

Welcome to the forum Jon, nice to have some more members from the area!

Many cameras have selectable cropping available in camera. A couple of members of our workshop don't have computers & rely on this when printing!!

IIRC some FF cameras automatically switch to crop mode with crop lenses. I hope they have an option NOT to crop DA images, the zooms will often give more coverage at some focal lengths, & cropping in post is not an issue for me it's something I do quite often anyway.

It's one of the reasons I prefer to use mirrorless cameras for long exposures. If it wasn't for the looks & lack of EVF the K-01 would be perfect!.

As others have said all full size Pentax bayonet mount lenses can be used with any Pentax DSLR. (Pentax has also made miniature 110 & Q series lenses which can't).
Third party K mount lenses are also fine.

There are limitations with older lenses - the camera can only control aperture on PKA & later variants (A series manual focus, & all auto focus lenses).
Earlier K & M series lenses (PK mount) with no electrical contacts on the lens mount, need the aperture set manually on the lens, stop down metering & a menu setting changed to allow 'shoot without lens'.

M42, & T2 lenses can be used as PK mount ones with a suitable adapter.
Tamron adaptall2 lenses can be fitted with either PK or PKA adapters & then work as those lenses.

If you end up getting one of the PK-R lenses davern warns about the offending pin can be removed (or filed down) making the lens usable safely.

When the new Full frame camera comes out some of the current DA lenses will not give full sensor coverage - all the older film lenses should be OK.

Happy Christmas everyone!