Starting Issue

Manual Transmission - V6 2.5L
I've been having a starting issue on my ford probe. I just replaced the battery not that long ago and checks fine (also lights/windows/locks etc work), alternator has been testing good for the past year, starter was literally just replaced, and my issue still persists.
When I turn the key in the ignition, the engine cranks but does not start. Before the starter was replaced the engine would crank and would rumble as well like it was already started, but wouldn't turn over 'sometimes'. After the starter was replaced, it started fine and I was able to drive it. Though as soon as I parked and went back to start it, I couldn't start the engine again. Took it all night to finally start it. Now, it's either a hit or miss whether it starts.

I experience no symptoms while driving; no rumbling, no sounds, no strange occurrences, etc. The only thing I have witnessed is that on a rare occasion, the check engine light would display while driving. However, usually this happens while in gear and if I shift into neutral, then go back into gear and as soon as I give it gas; the check engine light will go off.

The shop I took it to said that there is something inside the distributor that is going, causing my issue; in which the whole distributor needs replaced. They said it would cost aprox. $700+ to replace. They said that it wasn't the distributor cap and the issue lies within the distributor itself. Since I have over 168,000 miles on the car and this is a big amount of cash to spend on this car, I'm wondering if it's worth the cost. I'm also worried that if I get this replaced / fixed if I'm bound to encounter other issues and/or if it will keep going for awhile longer.
I've spend more money on this car than I originally bought the car for, but is it worth fixing? I've done a lot of repairs on this vehicle.
Just to note: I have replaced the water pump, the timing belt, brand new exhaust, and others that I already mentioned. I have replaced other parts as well, nothing as major though, like brakes, calipers, and tires. So there has been a lot that has went into the car.

Any help, suggestions, or advice is greatly appreciated! Thank you in advance!
I have been relying on rides since and I need to get back on the road.