William Guy

Maybe there will be a revival of silent film!

Yes very helpful friendly members there, frequented the site for many years.
 
Here's a SMC Tak breakdown, scroll down below the Canon FD bit:
 
http://k10dpentax.blogspot.co.uk/search/label/Repair
 
And a short list ;-) of links to repair breakdowns and such:
 
http://www.4photos.de/camera-diy/index-en.html
 
Have you also tried pentaxforums?
 
http://www.pentaxforums.com/forums/54-pentax-lens-articles/179912-pentax-k-28mm-f3-5-disassembly-cleaning.html
 
Biggest contention I've found over the years has been what sort of lubrication to use for smooth focus and I settled on this, which has worked well:
 
http://www.ebay.com/itm/HELIMAX-XP-Camera-Telescope-Optical-Instrument-Focusing-Helicoid-Grease-w-PTFE-/271052175856?clk_rvr_id=631740458361&afsrc=1

This site is excellent for info on manual lenses and has good info on care and repair, getting a basic toolkit together and all that.
 
http://forum.mflenses.com/equipment-care-and-repairs-f6.html
 
http://forum.mflenses.com/basic-techniques-to-repair-lenses-and-cameras-t32862.html

I've opened a Nikon 50mm E Series prime lens and an old manual focus Sigma 80-250mm zoom lens (Pentax K). Neither of these were expensive, so it wasn't much of a risk. The 50mm E Series was easy to open up, and easy to get back together again.
 
The Sigma zoom however... I tried getting it back together for 30-40 minutes or so, but no matter how I tried assembling it, something with the zoom mechanism went wrong - I couldn't get it to zoom the whole range, just perhaps a third or a half of the original zoom range. It wasn't a lens that really mattered to me, so I didn't bother spending more time on it. But, from my own experience and from what I've heard from the camera service shops in town - zoom lenses in general are much more complicated if you need to open them up fully, and will take a lot more time to service.
 
Personally, I wouldn't open up any of my AF lenses. Even though I'm not fully certain that it is so - I'm expecting them to be more complicated and that there's a risk of misaligning something.
 
My own conclusion:
If it's older primes that aren't much worthy because of their current condition, I'd open them up and attempt service myself. Zoom lenses - I guess it depends on their design and what part of them that you need to service. The one I attempted service on had to be fully disassembled to clean the lens I needed to clean (oil spots). Had I not had to disassemble it entirely, it would have been a lot easier to assemble it since I wouldn't have needed to disassemble that zoom mechanism.
 
For cleaning elements, I'd ask some camera lens service shops. I asked at one of the local shops about cleaning coated elements here in Stockholm, and they were very happy about giving advice. According to them one of the best fluids for cleaning lenses (this was in the context of older lenses, I'm unsure if they advised it for only those or for newer lenses as well) was acetone. Before using something like acetone on a lens though, I'd strongly recommend to google around and find out more about the risks of using such a fluid for cleaning lenses. Here's one discussion about that at least: http://www.pentaxuser.co.uk/forum/topic/will-using-acetone-to-clean-a-lens-affect-smc-coatings--35361
 
Another good tip: Try to see if you can find some *very* cheap lenses in a second hand shop or such and use those for learning.

Andy, share you YT links! Would be nice. I have a lot of Minolta lenses, so the video below was very useful to me. Even if you don't have such lenses it gives you a good sight of all the parts inside.
 

No one has mentioned Nikkor AI and AI-S primes yet. I have a set of five, cine-modded by Duclos, and I have been pleased with them; first on my GH2, then on my FS100, and finally on my 5D3. I've also had them on a RED Scarlet, and they looked great at 4K. They are compact but well-built, and the lens characteristics match closely across the set. The only downside that I can think of is that the focus ring goes the other way, making a reversible follow focus a necessity.  
 
Here's a nice rundown on them by Caleb Pike of DSLRVideoShooter: