90 Reverse Gear

Hi - im trying to sort out reverse gear selection on my early 90 - it works ok but selects far too easily - mostly instead of first! Ive stipped off the tunel and gear lever cover, i can see that there is a fixed stop on the left for fifth gear, and on the right there is a plunger which i guess should be spring loaded for reverse.
my questions:
1 i cant remove the plunger untill ive got the socket for the gear lever off the end of the selector rod - ive removed the grub screw but its being a bit stubborn!
2 there is a brass plug which covers a drilling going down to the plunger chamber and i can see a rusty ball in the bottom - what should i find when i eventually get the plunger out and what is the purpose of the brass plug and chamber? - should this be oil filled as the plug has a gasket fitted.
thanks in anticipation

The bolly sits in a groove machined in the plunger, the further you screw the adjuster bit in, the harder it is to select reverse. The spring may have become sloppy or it may all be rusted up. There is no oil in the housing and the gasket is there to stop water getting in.

Take the whole thing off, take it apart clean it grease it and put it all back together again, bolt it back on adjust it and Bobs your aunt Fanny.

Thanks Grunt - mines just ot a brass plug rather than a screw and locknut but there is no spring beneath. As you suggested ive had it apart, greased the spring in the plunger ( i found out that the jiggly bit in the selector has a nylon bush when i warmed it up lol) greased my ball so to speak and put iot back together with a spring i found in my tool box - i couldnt then engage recverse at all. By taking the spring out and whacking the gear lever, i eventually disloged the ball and could get reverse. the same thing happens if i push the ball into the groove with a screwdriver - it seems to lock up. The ball is quite rusty - do you think that might be causing it to stick? thanks steve