Why am I experiencing gear clash in my transmission?

What is your question?

It started about three months ago, I was driving and started experiencing gear clash shifting from neutral into 1st and accelerating. I had to forcibly hold 1st gear in until I started moving, then I'd hear an audible (PINK) sound. So I removed the shifter and peered into the tranny and found the oil to be low. I filled it with Mopar 75W - 90 and went on my way. No change. I was beginning to think it might be mounting, but I have not a clue on how to check it. Now, I have the hard shift into first, smooth engagement into 2nd (upshifting and downshifting), hard shift into 3rd (I have to push it in fast/hard to get it to stay, but it stays 75% of the time with a good shove in), Fourth is completely inoperable with an occasional shift ~10%. Fifth works fine and reverse works. I shift from 1st to 2nd, to 3rd then to 5th, because my 4th isn't operating. I've also noticed that it'll shift into 4th a lot easier when the transmission is cold. So I'm beginning to suspect wear. I don't feel a 'hard" shift, but when I shift into the gear, it doesn't connect, like I feel ticking in the shifter and an audible grind. I don't hold it in, it's very distinct. Maybe my clutch is in need of adjustment, because I purchased the car and the parking brake is busted, so I'm in the process of repairing that as time allows. Any and all information and or ideas relating to the issue would be helpful.