My mom gave me this giant, old, plant recently and under my care since July he's going downhill. I desperately would love to save him as he's been around about as long as I have.

Background: This plant has received regular doses of water once a week of about 1 pint each. He has always sat near the window in a very small amount of direct sunlight. The temperature is always room-temp, so around 70 degrees, and he's grown leaps and bounds for over 2 decades.

My mom gave him to me in July, and he seemed to do well for a couple months, but until recently my mom didn't tell me how much water to give him so I ended up giving him a quart or so each time. Soon he started to look like he was being weighed down a bit, so I gave him about 3 weeks to dry out, but he only seemed to get worse. I thought maybe he was thirsty at that point, so I watered him again with about 2 pints, but his condition seemed to continue to deteriorate. My mom just told me she used to give him 1 pint a week, and that she doesn't know what type of plant he is so it's been tough to find out how to help him. It's been 2 weeks since I've given him any water, and his soil is still moist.

What do I do at this point? Pics are below.

Majicege, what you have is an Umbrella plant or Schefflera. It looks like it's been overwatered to me. No sign of browning leaf tips like you would see if it had been too dry. Don't water until the soil looks like it's dried out some on the surface.

Thank you so much for the response : D

So you think it's not like 'done-for' or anything? If I don't water it until it dries out, you think he'll make it?

looks like a tupidanthus

I was going to say about the watering too much maybe too..

but my question would be, does that pot/container have any drainage/holes?????

Looks healthy to me except for your watering.
Can you find out if this particular plant ever, eventually gets so root-bound that it may need to be replanted in a little bit larger pot with fresh new soil?

if the roots are too soggy for too long that can cause damage - regardless of whether the current pot has drainage holes or not.

it might start to rebound if it's taken out of the pot and the overly moist soil is replaced - you can put it back in the same pot if you find it's not rootbound on top of the overwatering or put it in a larger pot if it is rootbound. then you can get it back to the pint a week cycle.

We re-potted it about a year ago (into a bigger one), and I had to somewhat re-pot it when I moved it in July. The pot it's in does not currently have holes in the bottom, but I could change that easily with a turkey pan and a screwdriver ; )

The top soil is drying out, but deeper down it's still moist. At this point, do you think I need to goto lengths to fix this, or will drying it out for a while do the job? I'll do whatever I need to help out this big'ol plant, and thanks to everyone for the info : D

Lighting:
Moderately lit area, within 8 feet of a sunlit window.

Watering:
Water thoroughly, then allow the top 1-2 inches of soil to dry out between waterings.

After you drill the drainage holes, you can also loosen[aerate] the soil with kitchen fork or chopstick to allow oxygen to reach the roots. If you don't have square saucer to put under the pot, consider double potting.