Well,it seems you made several mistakes. Unless you intend to use PURE mineral soil , fertilizer use is optional. Its even not recommended if the soil is standard(peat +perlite). I use predominately mineral but not pure soil. 60-80 % grit+pea gravel, > 5% clay, and the rest is peat/vermicopmpost. Too much nutrients may lead to fungal attacks..

Second - this ones is important: DONT MIST CACTI. In fact, try to avoid wetting the plant body as much as possible. Water the soil only, and stop watering once water begins pouring out of the bottom.

Third: Out of experience, change the soil if it looks questionable. Most "second hand" or"home grown" plants are often sold if muddy topsoil. (if you think about it, whod use top of the line perlite and pumice and whatnot....), and mass production nursery soil has issues

Forth: Always check a plant for scabs or whatnot on purchase. If it unusually soft, black, mushy, or suspicious looking in general, no sale.

Melocacti can be hard to cope with, ive lost a few myself, and had to find out why. When i applied the procedure on similar problematic plants, the results speak for themselves.

Nice mature Melocactus. Looks like it has some corking at the base, that is fine as long as it is hard - it comes with maturity - as long as it is not soft. There are a few warty bits on the skin, but is your skin totally unblemished? Mine sure isn´t.

I don´t worry about pouring water onto the plant, that is what happens when it rains, anyway. I totally avoid the use of both peat and perlite, all my guys are in a predominantly gritty and well draining mix - but other growers use them with some success.

I have actually stopped growing Melocacti myself - my plants stay outdoors all year and whilst we are frost free it goes down to about 3 C in winter nights which is TOO COLD for them - they need a minimum of 10 C (50 F).

Good luck with it.

I don't think it is looking in good health and would not be surprised if it is rotting rather than corking.

Mature Melos are a pain to deal with when repotting. I have lost many of them. They may lose roots when repotted or they may die if you don't repot. I still have some mature Melos but have lost many mature specimens over the years and no longer grow them as one of my favourites.

What's with all the white dots on the body of the plant?

It is a rot spot, it looks out of place . Also, could it have scale???

We need this first time poster to get back and tell us if the brown bits are soft or hard. But lots never do.

Well, it does look out of place compared to the cork between other ribs. Its how it usually is on melocactus

Well let´s not keep going on about GUESSING what anything LOOKS - that tells us NOTHING. As I have already said let´s wait for feedback on how it FEELS from the OP. If it is soft - bad news.

But don´t hold your breath.

Lots of first time posters never come back - in which case any further speculation on this now BORING bit of brown is pointless.

Hey yall, sorry for the absence, yesterday was a busy one.

the 'corking' is firm all around, not a soft spot on on the whole plant. Thats kind of what prompted the post in the first place: it 'feels' fine but is looking rough.

no idea on the white spots, i was kind of love drunk when i saw it at and just went on autopilot.

as for the soil, like i said, it's not an ideal mix and not one that i would prefer to have it in, but i know for a fact it had been repotted the day before i bought it and was scared that attempting to change it again would just be a death warrant for the root system.

Well that is good news. And some of my more mature guys have developed some white flecks - which aren´t scale - maybe a kind of vegetable age spot?