M42 Mount 28mm Lens

I am looking for a 28mm M42 mount lens.

Why M42 mount? Well I currently have a 29mm F2.8 Zeiss Jena (yep for Praktica) but it no longer has the ability to change its aperture. Its stuck! Now I could have it mended (it is a nice lens to use) but is it worth the cost. We are talking about £40 minimum.
But you are still thinking "why not K mount, he has a few Pentax bayonet bodies?" Although occasionally I will still use my praktica, I do have extension tubes which are M42, and are great with the K adapter for "super" macro.
So I am looking for a 28mm Lens to replace the faulty lens and use on both the Praktica and the tubes.
Why a 28mm? Well one, it will replace an existing lens, and two, my other M42 primes cannot get close enough with the tubes (I have a Zeiss Jena 50mm and Cosina 135mm)

Advices please.

Funnily enough, I have spent this evening dismantling, cleaning, freeing the stuck iris and then assembling a 50mm f2.8 Carl Zeiss Jena Tessar.
I have done many of these and a few pentacon 50s, as well.
Those East German lenses are a doddle to work on. Never done a 29, but I would imagine that the construction would not be very different from other Zeiss Jena and Pentacon lenses.

Give it a go. - There's nothing quite like the smug self satisfaction you feel, after successfully repairing a broken lens.

If you can't get your CZJ fixed then I'd say the best 28mm M42 lens to pass through my hands was a Super-Takumar 28/3.5.

Having said that, if you don't mind an extra 2mm then the Meyer Lydith 30/3.5 is something of a legend if you can find a nice one.

Mowog, can you put some instructions together? I dont mind taking apart, as long as it goes back together again.

Type the following into google. http://oomz.net/tessar/

An excellent step by step guide, with pictures.

Good luck!

cheers mate.

Gives me a little project whilst my back get back in order this week.