How have courts interpreted the estoppel principle as applied to the statute of limitations?

I fully recognize that in Busching v. Superior Court (1974) 12 Cal.3d 44, 115 Cal.Rptr. 241, 524 P.2d 369, the court made clear that a plaintiff's consent to a defendant's request for an extension of time "in which to answer or otherwise plead" could not be considered a General appearance to avoid application of the Mandatory dismissal provisions of Code of Civil Procedure section 581a. But the Busching court was explicit in stating that this holding had reference solely to the statutory exception set forth in section 581a and Not to the exceptions which the decisional law had created.

In Carruth v. Fritch (1950) 36 Cal.2d 426, 224 P.2d 702, which dealt with the estoppel principle as applied to the statute of limitations, the court stated that " '(o)ne cannot justly or equitably lull his adversary into a false sense of security, and thereby cause his adversary to subject his claim to the bar of the statute of limitations, and then be permitted to plead the very delay caused by his course of conduct as a defense to the action when brought.' " (Carruth, supra, 36 Cal.2d 426, 433, 224 P.2d 702, 706.)