Coolant sensor broke and leaked on to wiring harness, control harness/module.

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My 2002 540i has 140K miles and have had it 4 years. It recently shut down on me and a place in Kennesaw, GA specializing in BMW's indicated the coolant sensor broke and leaked fluid into the harness wires, control harness and module needing to replace all of it totaling about $3K with labor and testing. Car is only worth about $5K so they suggested an alternative to just dry and clean everything out completely (which they say is not a guarantee to fix the issue, but would not replace the parts) and they would charge $650 for that. When this happened the car would either not start or start in a "reduced power" mode and only drive about 10mph. I could turn it off and let it sit for a couple hours and would start up fine again. Is the $650 clean and dry repair advisable and is this process known to work well long term? Any other suggestions? Thanks in advance for your reply.