Outer Limits 4x4 Board

Has anyone experienced trouble with the input shaft on series 1 disco steering boxes. I have on two occasions had to tighten the universal on to the shaft due to it slipping on the spline and on one occasian loosing steering completelty luckely only going 10km/h. I have now put a nut on the back of the universal bolt and no trouble for the past month, am i going to have to eventually remove the steering box to replace this input shaft??? or is it the steering uni at fault??
And also what size/tool do i need to inspect the oil on the R380 box tried an allen key but looks to have more edges on it?

Hi Rovernut, are you my nephew? I'm Roveraut!
Re You R380. the nut is infact a Torx head, 5.5 I think.
I had trouble removing mine as some one had damaged the head.
I Replaced mine with a standard 1/2''plumbing stop plug. Now i just reach up and use a spanner to un do it. No more fiddley torx nut!

T55 is the Torx No. Cost me $25.00