MG Car Repair: MGB Transmission Vibration, clutch disk, clutch repair

Question
I had a transmission drain plug leak so decided to resolve the problem and also change fluid in the process.  The car is a 1979 with 86,000 miles.  I purchased the car last year and have driven it about 2600 miles.  About 2 months ago I installed a new Master Cylinder for the clutch.  I probably have driven the car a 1000 miles since the clutch repair.  Back to my question. After changing the fluid I took the car for a drive and now have a " vibration " in second gear.  It almost fills like the clutch is slipping.  The condition is only in second gear.  It's not real intense but I have drived the car enough to recognize something that wasn't there before.  I see some forums that mention gear box mounts and other possibilities.  Not sure how I caused this problem.  When I lowered the car off the jack stands I released the jack harder than I should have.  Could I have done something to a mount ?  Or should I rebleed the slave cylinder?  I am mechanically inclined but not a mechanic your help would be appreciated.

Answer
Hi Don:

I doubt that changing the clutch MC has anything to do with the "vibration" you sense. I would as you have already thought about, check the engine and transmission mounts as a bad mount could cause this problem. I also doubt changing the trans fluid had any negative effect- just check the oil level to make sure it is where it should be. At 86,000 miles you could be due for a new clutch disk and release bearing if it has never been changed. Parts are not expensive, but it is a bit of a job to install them. If you decide to do it, make sure you have a workshop manual or a Haynes manual - take your time and work safely! If you have a specialty shop nearby that works on MGs / British cars you may want to take it to them for an opinion as well.

Good luck with this!

Brian