If this was something you bought used from someone more than likely they plugged something into channel 1 and blew out that channel.
Which is always the first channel somebody messes up and plugs in the wrong thing to!...Then they sell it!
Check channel 1 all by itself with a known good signal with a known clean tape and make sure everything on that channel is setup correctly. (i.e. mixer levels, pans, switches etc.)
Record several seconds on that channel and then do the same for each of the other 3 one after the other.
Play the tape back and listen to each one separately.
If possible find another unit to play the recorded tape on which could rule out some things...that would be ideal. That way you might be able to find out if its the record or playback heads or a bad channel right away.
If channel one is the only one with distortion, then the next step is to look at the record and playback heads with a nice intense bright light and a magnifying glass.
Make sure they are shiny like glass and have no scratches, pits or damage of any kind especially at the edge of the heads which is where track 1 would be.
If the heads all look good then channel one probably has some blown or shot electronic component.
So then it a matter of finding that and fixing it, which for what it's worth I wouldn't bother.
If the head is damaged then look for a replacement, but usually you'd have to replace the entire head assembly and once again not worth it!

Is there a cheap alternative for playback only? I recorded all that stuff years ago, and I only wanted to see if there was anything decent on em. I could always get another 4 track but I kinda dont need it.

It would need to be another Tascam PortaStudio with the same 4 track head assembly to get anything useable!
I've stuck 4 track cassettes into regular cassette decks but the speed will be wrong (those Tascams are 3-3/4ips) and you'll probably get weird multiple tracks going on, but it won't hurt anything and it might be coherent enough to figure out what it is....doesn't help though!
I assume you still have 3 tracks working so you should be able to play those back and just turn down or turn off the bad channel?
You could pick another one up cheap for like $40-$75 on Ebait and then either make one good one out of the two or get lucky with the new used one! That's probably your best bet! That way you have parts!
Hope that helps,,,good luck!
It's always fun listening to old pieces that have been lost to the ether!
BTW...a Tascam 414 is 4 track not 8

Oh yea it is 4! I remember bouncing tracks back in the day on it and must have gotten mixed up....oh well. I kinda figured getting another one was the only way. At least its cheap since its old right! Thank god its not considered a classic recorder and is worth more!

Ok I was just reading up on tape deck maintenance, and I've been reading about demagnetizing.
Could that be a possibility? The article was sayin that after prolonged use, excessive noise and loss of high frequency's can occur? Maybe...?

If you are getting the distortion on track 1 when replaying tapes that you know are OK, then the problem is not on the track 1 input, it's in the replay chain.

What I would do is use an unwanted tape and record the same signal on track 1 and another track. If you can run a signal generator program on your computer, output a 1KHz sinewave through your interface and try recording it at different amplitudes. Use your DAW to examine the replayed waveforms and see whether you have excessively more distortion on track 1 than on the other track. If the answer is no, then your recorded tapes have deteriorated, probably by being exposed to a magnetic field on the face where track 1 is.

Using a demag probably wouldn't hurt but just adds more cost to buy one of those and then find out that's not the problem with track 1.
If you can record a signal like Boswell said and check the waveform in your DAW that would be a great way to figure out if the record head/electronics are bad or the playback head/electronics are bad.
If you haven't already tried my quick test.
Still I think unless your a tech wiz and can troubleshoot and replace caps and transistors and have fun at it....your better off finding another unit....You can always sell them back on ebait after you get what you want out of them!
My guess is a demag is about $20-$30 and a used deck maybe $50. Also Check Craigslist in your area if you have that....sometimes you find them in the classifieds under "musical instruments" or "electronics".