MG Car Repair: cant get to reverse, reverse light switch, forward gears

Question
QUESTION: I have a 1969 MGB. 59K miles. Excellent condition. I can't get into reverse.
Flushed the tranny twice. If its hot and I really bang it, sometimes I can get it
into  reverse...all forward gears are perfect..thoughts??

ANSWER: Brian, You can't get it into reverse because of gear clash? or do my mean the shift lever will not move? or do you mean the lever moves as though it is shifting into reverse but there is no reverse there?

---------- FOLLOW-UP ----------

QUESTION: I can't move the shift lever thru to the left to engage reverse. If I slam the
lever repeatedly and hard enough, once in reverse, reverse works fine...its
getting the lever to go there

Answer
Hi Brian,
There is a strong detent that must be compressed to access reverse. It may be dry and need lube. It is inside of the gearbox tail shaft housing. First do this to be sure it is harder than normal. Put the shift lever in neutral with the lever over to the right side of the "H" pattern then with your right hand about 6 inches to the right of the lever, HIT the lever with an open palm all the way to the left and hold it there to see if you can knock the detent in, then pull back to see if you entered the reverse pattern. This is the normal method to enter reverse. If it were easy to enter the reverse pattern it would also be easy to enter reverse when downshifting from third to second going into a tight turn and thus destroy a gearbox. Practice this a few times and if you still can't easily enter reverse pattern you will probably need to remove the engine and gearbox and remove the shift tower to access the detent. It is also possible that a reverse light switch is faulty and making it hard to enter reverse.
Let me know,
Howard