Every enlarging head has its foibles.
Make a gray print without negative but in focus. If you get marbled uneven look, ask yourself if this would be aesthetically acceptable as an overlay to all your prints (because it is there).
You might be able to obtain two cold light heads for a couple hundred dollars, if both work you have a spare. Cold light heads present a "time" challenge, there are compensating timers to solve that or there are strategies (like leaving the light on).
Color heads are going to be diffuse so they make a good choice.
Also, make sure you are not stopping down more than you need to. Most recommend 2 stops from open, max. This is the sharpest place for many lenses, and stopping down more than that, you may be picking up too much depth of field, up into the condensers.
so far so good with (a combination of) new condenser lenses, and a bit of rotating... i havent tested anything above using a 50mm on 8x10 with 35 negs... no specks or scratches in the shadows, afraid to test with a grey print though! printing with a 2.8 rokkor lens, usually find myself printing at 8 and mostly 11, subconsciously over-correcting for misalignment issues that I'm not even sure are there!
would love to get an aristo or zone iv, but saving for a proper medium format kit before that happens...