Stuck in diff and gears getting tough to engage.

Hi,

I've got a bit of a problem with the diff lock and gearbox on my manual 98 300tdi. I'll try and explain the best I can...
Ive done a couple of pay and play days with my disco... the first time I went my gearbox was fine but I was informed my diflock was jumping in and out.
The second time I went my difflock was fine and engaged ok but I noticed trying to get reverse was getting difficult (although it was better in low range). Nothing broke on the day, which I was very pleased about

While checking my disco over the other day I engaged difflock and as I did the lever seemed to 'clunk' in but wouldn't come back out. Although it will still change between high and low. I've used reasonable force but don't want to break it (anymore than it is)
Ive spoke to a friend who reckons the gears bit could be the clutch on it's way out. But is stumped with the transfer box? The easiest thing would be to replace the transfer and gearbox and clutch but i've already spent a fortune on it in a few months a the missus is on my back

Has anybody had similar or can shed any light on my problems?

mine use to be a bit of a bastard to change, but a mate found out if you stop on a bit of a slope and let it roll back then try it you can change the transfer box alot easier