I have a 25 gallon Fimco sprayer that is approximately 5 years old and I only use it a 3-4 times a year. I store it inside and always rinse it out after each use. Now for the problem.... It recently lost pumping pressure... It has always held 60 lb psi and when spraying would drop to 40 but now it will only pump to 40 and drop to 10-15 when spraying... I have checked and cleaned all lines and filters and replaced check value in pump... I have also connected to a water hose and it pumped to 60 and dropped to 40 when spraying. Any ideas on what to check next?