Diesel Engine Specific Aid

I bought a 1978 300CD with 250K miles about two months ago. So many problems and I've never worked on a diesel but my income is too modest to afford a mechanic. I'm just a humble computer guy. Okay, enough blathering. Recently, the power assist on the brakes gave out and, simultaneously, the car wouldn't shut off when I removed the ignition key. I have been told that I need to rebuild the vacuum pump. After a week of manual braking (that thing's a beast to stop) and manually choking the engine when I get to my destination it's developed a new problem that is far more devious.

I have a newly purchased 300cd non turbo that has a significant exhaust leak from the top of the manifold. Do these run gaskets on the exhaust side? I could not find them listed online. Are these prone to cracking and warping, or should a gasket do the job? Should I bother trying to retorque everything on my badly leaking gasket?

Hi there. I have a 300DT Euro with a 4 speed manual. I bought all the clutch related parts to do the job and then decided to have my mechanic do the job.
So we after the installation, all was fine for about 1 week, then the shifting became hard. I took it back and he figured their was some air in the lines still. So he bled the system again, getting a little bit of air out. Then another 2 weeks later, the same thing happened and i took it back again. And now the same thing is happening again.
I don't want to take it back to him again. I trust him and his work, but i would feel wrong in asking him to 'fix it again'. Also, Mercedes are not his specialty, so i am asking for advice from Kent or anyone who has any help to offer.

My 1985 300cd started acting up today. Car runs great... however today the Car did not start. I insert the key, turn the key to show glow plug lite on, wait for light to go out and then turn key. the key does not turn ( i mean it will not rotate clockwise anymore). Then i will rotate key back to off, pull key out, cycle the transmission from park to low to neutral several times. Then insert key and try again and sometimes it starts and sometimes it does not. Basically i Keep doing this procedure till it starts. After i start the car i drove the car 40 miles with no problems.