This question already has an answer here:
Company I worked for recently inherited a custom CMS system that is extremely buggy, no documentation, and unreadable logic in everything. The client will not have the budget to re-platform for another 6 months or more.
The issue we are having is fixing bugs generally requires either patching it or completely rewriting the entire functionality/feature and is extremely hard to estimate time.
Should we continue to patch until they re-platform or refactor entire functionality and add documentation?