The 206 drive shaft was susceptible to a boot split and loss of grease, had one happen to me but I found it between flights and grounded the machine. The tel-a-temp stickers were usually an indication of overheating, as long as a clumsy mechanic hadn't knocked it with a spanner and turned it black.
The all-metal Meccano-style replacement has also had some failures, but not from lack of grease.