You sure you have the same engine? Disco Engines don't go to 250k..do they?

Actually, it sounds like you have a solid motor for the amount of miles. i'm hoping your tick is something due to wear over time, and nothing critical like a slipped liner.

I will consider myself extremely fortunate if my Disco has your problems in 150k miles. (I'm at 105k currently)

 

I've gotta admit 250K on any vehicle is amazing......

 

1. I have no idea. Does it change when you hit the brakes?

2. I bet the ticking is something in the valvetrain. The flat tappet cams in these trucks are prone to wear, and they wear the lifters also. With 250k miles, the cam has got to be tired.

3. The lines that run trans fluid up to the cooler leak on my truck. I figure the fittings are loose but I've been too lazy to check them. Are you sure it isn't power steering fluid? The hoses on these things tend to spring small leaks and make a mess.

 

the tic you can search and come up with a 100's of things people have replaced trying to get rid of that tic.
At 250k it's probably worn valve train, but check your oil pressures hot and cold, the reason is a cracked oil pump gear is fairly common, and it is one of the causes of a tic.

 

Are you sure the noise is not the normal t/c whine?