My opinion, and you are not going to like it...
VFDs don't "slowly get bad" in my experience. They work fine, until they don't work at all.
MOTORS on the other had start to fail slowly. In this case I'd venture a guess that this motor was NOT built as "inverter duty" because you added the VFD to it after the fact. So it's entire more likely that you have created a turn-to-turn winding insulation fault inside of the motor due to the voltage stresses created by the VFD, a well known phenomenon called "reflected wave" or "standing wave" insulation damage. It's not very common in 240V motors, but it IS common in 460V and it VERY common in 575V motors that were not designed to be run from VFDs.
The pulses in the PWM pattern that the VFD uses to create a 3 phase "pseudo AC" output cause the conductors to act like capacitors and create extra voltage pulses on the conductors that travel down the wires until there is an impedance change, i.e. the motor terminals. Some of them get reflected back the other way, where they combine with new pulses and then hit another impedance change, the drive terminals, and reflect back again. Even though these extra capacitive voltages are small, the constant reflection and addition back and forth (like a slinky wave) eventually become VERY HIGH voltage spikes that can exceed 3x the line voltage! So on a 230V motor, the insulation is the same as is used on a 460V or 575V motor; typically 1200V because it is 2x the normal voltage (575). With an inverter involved, 3x 230V is still below that value, but on a 460V motor that 1200V insulation is lower than the common spikes by 180V and
on a 575V motor those spikes can easily be over 500V higher than the insulation value of the windings.
So what happens is that where the insulation is thinnest, usually the "first turn" where the motor leads connect and go into the stator slots, the insulation fails between winding conductors on the same winding, effectively lowering the number of turns in that winding. That then causes the current to drop, reducing torque. But the motor will still TRY to do it's job, so slip increases, the motor draws more current, and that winding situation keeps getting worse and worse over time.
The result is OFTEN a cascading increase int he number of Over Current trips in the VFD as the windings fail.
Here is what that looks like inside of the motor:
Bottom line, I think your motor is toast and buying a new VFD will not change a thing. A 1HP motor will cost more to fix than it will to replace. But when you replace it, use a motor that is DESIGNED to be operated by an inverter. What they do is use insulation that is rated for 1600V (or even higher in some cases). You could have ALSO used what's called a dv/dt filter on the output of the VFD, but it's too late for that now.