[TR] TRiumph 2 questions

[terryrs at comcast.net]

Man, the List is back online just in time!
 
1)  I've just blown my manifold gasket for the second time, both about 8,000 miles.  'Course, I admit, I drive 80 MPH on the way to work every day, and once hit 100 passing a car that decided to speed up while I was going by...you know the type.  
 
The inlet and exhaust manifolds are not buggered up, and I've been able to get good leverage on the bottom nuts.  
 
So...is there any special manifold gasket or trick that can keep me from having to go through this each year?  
 
2)  Wavering speedometer.  I had my speedometer (and other gauges) rebuilt by MO MA.  Now the speedometer is wobbling back and forth over a 15 mph range while I'm driving.  Oddly, it seems steady when the car is cold and at lower speeds.  Could the speedometer transmission sending gear be a problem?  
 
Glad to have you back, all.
 
Terry Smith (TR3A TS 58667)
New Hampshire