How is the shutter on that Praktica B100? I had a BC1 back in the mid 80's that broke in just over a year of use & wanting to give one a try again, have just gone through another two from ebay, both of which were broken. One, no matter what you film speed/aperture/shutter combination set always claimed overexposed. The other would only fire the shutter at one speed no matter what. Have read horror stories of how unreliable the Praktica bayonet bodies were & that there were bins full of broken bodes. Shame really as the Pentacon glass is often quite good.
Decided against trying a 4th BC1 & have listed the lenses on ebay. Like your MTL50 much more

Been thinking about getting one to keep my MTL5 company.