Well, I am new and am still waiting for parts for my Mcal.
It needs some descaling, but I ordered the parts for it. New pressure gauge, thermostat, pressure valve
You think just descaling might fix it?
What mixture should I use?
Here are some pics




Go myself a custom tamper made locally
The one with the filled holes

I just went through one a few weeks back. I used 50/50 water and white vinegar. I filled it, let it sit awhile and then poured it back out the fill hole into a bowl to see if there was any chunks or foreign matter. I filled it again several times and let it heat up then pulled the lever and let the mix run through the pickup tube and group. During these phases the water was coming out blue indicating there was some scale. Third or fourth fill the mix came out clear so I quit running vinegar and just ran a few tanks of clear water till I couldn't smell vinegar anymore.

You can get an idea of whats in the boiler by shining a light down the fill hole and looking in. You should be able to see the top few coils on the element.

Also if you have buildup inside the porta filter be careful about lengthy soaks in detergent as it could remove the clearcoat that protects the finish from tarnish on the outside.

So how long should I have the vinegear in it?

I left mine in 4-5 hours first fill and about an hour on subsequent fills. I don't think there is any hard and fast formula. I suppose a lot depends on how bad the scale is. Mine wasn't bad at all.