Problems with my new E39 Heeeeeeeeeeeeeeeelp

[aabdelhamid]

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Help I just baught a 97 E39 523i after driving my lovely 520i E34 1990 for a long period (thank god I did not sell it yet)
I have the following issues in the E39 and need guidance:
1) The computer does not detect the car by any means when connected to code the engine and gear box, it cannot communicate with the car and would not allow even recoding at all. Help me what can I do
2) The brakes when driving are mushy, the pedal sinks when the car is running and I brake and when the car is stationary and engine is not running the brakes do not sink. I am sure this is the servo, but what should I check exactly
3)The exhaust sounds like there is something loose, I checked everything and all rubber and bolts are OK. When I kick-down the exhaust sounds like a grinding wheel for a while ... any insights. I plugged the exhaust at the back and there are no leaks as far as I hear
4) The fan clutch is OK when the car is cold but once it heats up, the clutch does not disengage at all. My understanding is that the clutch engages till the car reaches a certain temerature and then it cools down the clutch soit disengages for a while and then engages again.

Please answer each one of those issue seperately as Iam just about selling the da.. thing again.
Thanks in advance
A very sad newly acquired E39 owner.

[632 Regal]

#1 Huh?

#2 Probably the master brake cylinder.

#3 might be rubbing somewhere under the car.

#4 The clutch fan ALWAYS spins, just spins harder when hot.