The obvious likelihood is the Turbo seals, followed by valve stem seals and any oil leaks,
Rear main ? Front crankshaft seal ?
How many miles / kilometres? On the clock,
If you don’t have definite proof of change then that would be my first maintenance job
Before using her,
It’s not just mileage it’s also time and possibly contamination ( fuel/ oil /water)
Get it done
Yes I had to repair mine as no suitable replacement was available, I brought new end caps as there was no way to salvage them,
Then quite a bit of 1/8 plate to repair finish with Matt black,
I see you are a 200tdi defender but should be the same, and if you check the archives you will find
People who have used the 300tdi turbo units on the 200tdi engine,
No it shouldn’t go to the floor, with servo working it will drop slightly but stay firm,
Check for leaks? And if nothing shows it’s more than likely the master cylinder creeping,
Replacement recommended, straight forward job,
When I overhaul my braking system I replaced all the pistons with stainless ones with new seals,
The old steel pistons where heavily corroded but the bores where ok,
Another possible problem are the flexible front brake pipes, I replaced all mine but if yours have partially
Collapse internally...
Are you sure the noise isn’t from the exhaust cooling down after you have screwed the arse of it?
Pop the bonnet as soon as you stop and locate sources,
Check the top of the sender unit, very weak point when rusted, I would take the sedimenter apart and give it a good clean, replace both O rings while you are there,
How much of a rebuild? Valve stems seals are a likely candidate, did you replace pistons or rings?
Where the bores honed? And obviously injection pump timing needs to be spot on, injectors get blocked and out of calibration,
Crankcase vent system also can cause blue smoke if blocked plus oil...
While the hub is off I personally would check the bearings clean them and repack with new grease,
I used Castrol LM grease, it’s all straight forward except removing the front seal can be a bit difficult
But I was going to change them anyway,