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So if you guys can help it would be really appreciated.
The turbine/input speed sensor is behind the valve body. Valve body needs to be removed to get access. Link below to a project I did a few years ago that will show you it's location.

DIY: ZF 5HP19 transmission: Valve Body

The transmission generally goes into limp mode when there is an electrical fault detected. It won't go into limp mode when it senses slippage. It will shift to another gear and attempt to use other clutch packs. If it goes into limp mode due to major slippages on multiple clutches and it's out of ideas, then it will always start normally once the engine is restarted and then only return to limp mode after it detects the failures again.

If you have an input speed sensor failure that will put it into limp mode the moment it has been detected. If it has been intermittent, I suspect it's not the sensor itself that has failed but some sort of electrical connection issue that is causing a disruption to the signal.

Limp mode by itself feels like major slippage is happening. It's stuck in 4th gear and the TC clutch isn't engaging. It feels like there is a big rubber band between the engine and the wheels. Especially from a standing start where the revs go up and nothing really seems to happen except for a very gentle acceleration. If this is what you are experiencing then I suspect what you think is slippage is just normal limp mode behaviour.

Here's what I suggest:
Disconnect the plug at the transmission and clean all contacts. There are two plugs. One goes to the valve body and the other goes to the switch on the left side of the transmission. I'd clean both but the one at the rear that goes to the valve body is the one that might be creating the issue. Often you can get some oil creep in here over time that creates connection issues.

Buy a BMW K + D CAN cable off ebay and install BMW tools that is available for download here on the forum. Use INPA to look at the transmission control unit and see the errors after initially deleting and then getting the car into limp mode again. This is going to be the first step in diagnosing the issues.
 
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