Hmm. Just to warn you . I changed the speedo cable after it broke - shortly after getting the car - and hoped it would fix that annoying knocking sound that sometimes comes from the instrumentscluster (frequency of knock proportional to car speed), but unfortunatly it didn't.
Maybe you have the same problem, and it seems to be within the speedo itself.
Regading the dipstick - i was very carefull with this when rebuilding my engine, as a friend of mine experienced that the dipstick of his TA was too short. He replaced it, and the new one was eaten by the cranck - also apparently because of the internal guide tube being left out during a privious repair.
There is indeed an internal part of the dipstick tube, that guides the dipstick to the buttom of the oilpan. Unfortunatly i can't think of a way to check if it is in place, without taking the oilpan off, but i could measure my dipstick (sorry, no sexual reference intended
), so that you may verify the length.
The internal tube fits in a hole in the bottom of the block, and is bend about 45 degrees.
I think that the tube was held by only one screw, so it may be at the bottom of the oil pan.
-Christian