violent jerk

Thanks for that! Those bevel gears do feel like the area where the slack is. That's a good idea! I've often wanted to treat myself to an endoscopic camera, this could be the excuse I've been waiting for! 
If I can reach it with out taking the engine out then I'll give that a go. 

For what it's worth:  My 1300 has 109,000K.  Never had the transmission apart.  It can be shifted so smoothly its like an Automatic !
This is the backlash. Approx. 42mm/1.675"
The colors are as follows:
Red = 1st
Black =  2nd
Green = 3rd
Blue  = 4th
Yellow for 5th doesn't show
 
 

Thanks Scotch. That's great!, I'm going to try that today and see how it compares. Re mileage I suppose one can't be sure what a previous owner has done or even if mine still has it's original engine. or clocks. It is still on it's original bore, I do know that. 

Well that's strange! I did your measurement Scotch, and also came up with 42mm .  Now I'm really confused. 
Maybe I'll take it for another ride just to test the take up clunk.
 

 "Now I'm really confused. 

"
That's why I get paid the Big Buck$