What are signs of the clutch/overdrive starting to slip ? Car bucks every so often & I feel a clunk in driveline.Cars is '82 244 4+OD 160K+ miles.

Signs of clutch slippage don't include bucking and jerking. When driving at a highway speed and you accelerate the engine will rev up but the car's speed won't increase at the same rate.

I had a slipping clutch a few years ago due to a massive oil leak, which went away after the leak was fixed and everything dried out. Also my car being a turbo the clutch slipped very heavily during any sort of boost.

You might also want to check the clutch adjustment.
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Zack Silver 83' 242Ti (217k)

Sounds typical for worn universal joints in the driveshaft, especially if you get clunks when you change from forward to reverse or vice versa.

If it bucks starting to drive from a stand still that might indicate your universal joints are LONG overdue, and should be changed as quickly as possible.

You can easily check this by (for each u-joint) grabbing the driveshaft on both sides of the joint and trying to twist them in opposite directions to detect play in them. If any of them is really badly worn, it should be evident.

Should not be expensive to fix either, certainly not compared to changing a clutch.

The bucking/clunking in mine occurs while driving, and typically while in gear, rather than immediately upon switching gears. For example, I'll be driving along in second, and it does it. Could this still be the u-joints?

I would guess it is less likely to be the u-joints in that case, since it would probably originate in the engine if it does it at constant throttle. Do these new-fangled 240s still have a throttle position switch that can wear out, like the D-jet engines in 1800s and 140s?

Anyway, checking the u-joints is a 5-minute task if you can get your car up in the air a bit.

A month or two back, I was accelerating and the car started bucking until I eased up. Checked the plugs and found them fouled.

Turned out that I had resistor plugs as well as resistor (radio suppression) wires. (No warning is given when one selects plugs and cables about mixing the two.) Too much resistance causes weak spark leading to fouled plugs and misfiring.
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1980 245 Canadian B21A with SU carb and M46 trans

My car occasionally does the same thing. I feel like the drive shaft "clunks" and bucks. I'd be interested in learning what this might be as well.

One of the first places a clutch slip or weak pressure plate will show up is when you are in a higher gear and step on the accelerator, the engine will increase in speed but the car won't for a few seconds, then it catches up. When it is worse, the car takes longer to catch up or dosn't catch up at all. It should not make the car buck. Many times when you are in a lower gear it won't show until it gets bad.
Check your adjustment for free play if you have no free play , you have constant pressure on the clutch and it will act like you are driving with your foot resting on the clutch pedal.While you are at it check to see that it is dry at the flywheel, oil on a clutch disk can cause problems such as slipping, chatter when engaging and so forth. If you replace the clutch..replace it ALL....pressure plate, clutch disk and throw out bearing. I have seen a lot of problems from people that tried to save a few bucks and didn't replace the throwout bearing and had to go back a short time later and replace that. Check the flywheel surface for even wear while the clutch is out. It should be reasonably smooth, dry and clean. A little lubriplate on the center bushing helps both assembly and keeping the wear down but don't use too much as it can migrate out and get on the clutch disk.
Hope you have just an adjustment problem and not a clutch problem.
Dennis

One of the first places a clutch slip or weak pressure plate will show up is when you are in a higher gear and step on the accelerator, the engine will increase in speed but the car won't for a few seconds, then it catches up. When it is worse, the car takes longer to catch up or dosn't catch up at all. It should not make the car buck. Many times when you are in a lower gear it won't show until it gets bad.
Check your adjustment for free play if you have no free play , you have constant pressure on the clutch and it will act like you are driving with your foot resting on the clutch pedal, and while you are at it check to see that it is dry at the flywheel, oil on a clutch disk can cause problems such as slipping, chatter when engaging and so forth. If you replace the clutch..replace it all....pressure plate, clutch disk and throw out bearing. I have seen a lot of problems from people that tried to save a few bucks and didn't replace the throwout bearing and had to go back a short time later and replace that. Check the flywheel surface for even wear while the clutch is out. It should be reasonably smooth, dry and clean. A little lubriplate on the center bushing helps both assembly and keeping the wear down but don't use too much as it can migrate out and get on the clutch disk.
Hope you have just an adjustment problem and not a clutch problem.