SOS: Orchid that's had a series of problems from root rot to dryness to black spot

[thegirlwiththemouseyhair]

OK, this post is basically an SOS for my first-ever orchid, Oscar, whom I have named and refer to with human pronouns and basically treat as my pet; I have had my poor Oscar, an impulse buy from the grocery store, for a little over a year and a half, and this was practically the first plant I ever kept. Oscar is a Plainview Colorfuze orchid, and I believe is a phal although the Plainview Colorfuze website makes it hard to find out the species - maybe they treat it as too obvious to mention?

Anyway, everything was going swimmingly until this September, when a cousin helped me re-pot Oscar from the initial medium to a new one that was packed with a lot of moss. I didn't change my once weekly watering schedule for a few weeks, when I started to suspect I was over-watering. I tried spacing out waterings but by then Oscar had some root rot so I bought a different medium that is all bark, trimmed off a lot of dead, dried roots (super sad, because he had this beautiful network of roots which I lost so much of), and re-potted him again. The fiasco with the medium that was retaining too much water lasted from mid-September to Halloween, so about six weeks.

Lately, I fear I've been struggling with the opposite problem. Because this newer medium drains so well I'm struggling to figure out how to water often enough, and have started using the skewer technique I saw on this board as well as Google calendar reminders to water every five days (I read an estimate online that exclusively bark mediums may dry out every 4-6 days). Oscar greens up when I water, but looks pretty 'eh' otherwise.

Finally, to make matters even worse, I noticed last week that one of the three leaves left had a big black damp spot on it. I cut that whole leaf off with sterilized scissors and applied cinnamon to the cut to stop the spread of any infection. However, the part of the crown that that leaf jutted out of has really yellowed and dried up a lot in the last few days, and I'm worried about that.

Is there any way to save this orchid or should I start preparing myself to get an Oscar the Second? (I've just worked so hard to save this one, which means a lot to me...) I live in Montreal where we are going through a bitterly cold winter, so my condo is dry and static-y from having the heating on all the time. My place gets quite a bit of light, and I have started keeping Oscar by a window to try to simulate a fall/winter rest in cooler temperatures, although indoors in Montreal in winter is no rainforest. Also, I always water from the top which seems especially necessary now after I lost so many roots. Thanks in advance for any help you can give!