Gareth, we have all had problems with our printers. Be glad that your 1500W is relatively cheap.
About 4 years ago I lost a 7600 to a head failure. I tried on and off for a year or so to revive it, including replacing the head and various other parts, before finally giving up and giving it away to a guy who wanted it for parts. I replaced it with a Canon ipf6400 which had a weird problem right out of the box of sometimes depositing faint fuzzy lines on the back of a print. For the first year Canon did everything short of replacing it to try to fix the problem including sending an engineer who made a small modification that seemed to help for a while. But after the 1 year warranty period they refused to do anything more. I gave that one away too.
A little over a year ago I picked up a used 4880 with the intention of using it for Piezography. Jon convinced me to wait until PiezoDN was ready, which I did, but when going through the ink replacement process last summer, it suffered a complete electrical failure. Nothing, including replacing the power supply board has shown the slightest sign of reviving it. I replaced it with a refurbished 3880.
A month or 2 ago I was doing a routine cleaning of that 3880 and when I moved the head away from the capping station to clean the cap and wiper, I noticed a loose hunk of plastic with a thin metal bar attached at the far right of the cap assembly. Eventually I was able to determine that it had broken off of the top right rear of the carriage assembly. I have no idea how or when. Fortunately, the printer is still functioning well. I also have a second 3880 that runs the OEM color inks that has also been flawless and trouble free.
The 1430 (same as your 1500W) that I started out using with PiezoDN last spring, and which I was still using occasionally for experiments, gave an error when I turned it on one day about 4 weeks ago. Somehow it is no longer recognizing when the head is in the home position, and refuses to do anything. I have not been able to solve this riddle and gave up after a couple weeks. I just replaced it with a refurbished one for $200.
On the other hand 2 3800s that I had for a long time are still chugging along in the hands of new owners. I replaced the entire ink supply system in one of them.
The point of this tale is to suggest that you don’t give up. There may be some problems that can’t be solved, but most of them can if you have the patience to persist.
Transparency film is the most unforgiving of materials, and printing negatives on silver paper is going to reveal even the minutest of flaws. My next suggestion is to make some K-6 prints on glossy paper (since that is most similar to film) and examine them very closely for any of the symptoms you are seeing.