In this paper Behavioral Analysis of four units system with preventive maintenance and degradation in one unit Post Failure and the other units with perfect repair using Regenerative Point Graphical Technique (RPGT) is discussed. Initially, the Four units A,B,C& D are working at full capacity in which unit A may have two types of failures one is direct and second one is through partial failure mode, but unit B,C and D can fail directly. There is a single server (repairman) who inspects and repairs the units when need arise. On partial failure (before complete failure) server repairs the unit and on complete failure the unit A cannot be restored to its original capacity i.e. it is in degraded state. Fuzzy concept is used to determine failure/working state of a unit. If the server report, that unit A is not repairable, then it is replaced by a new one. Taking failure rates exponential, repair rates general and taking into consideration various probabilities, a transition diagram of the system is developed to determine Primary circuits, Secondary circuits & Tertiary circuits and Base state. Problem is formulated and solved using RPGT. Repair and Failure are statistically independent. Expressions for system parameters i.e. mean time to system failure, availability, number of server visits and busy period of the server are evaluated to study the behavior of the system for steady state. Particular cases are taken to study the effect of failure and repair rates on mean time to system failure, availability, expected number of server visits and busy period of the server. Profit optimization is also discussed. System Behavior is discussed with the help of graphs and tables.