Clutch slipping on 93 Honda Accord

I don't understand what happened as soon as you let out the clutch. Did it start to slip?

many modern transmissions use a 30 grade straight mineral oil in the box but experience shows that a 80-90 grade OEP oil is still the best for long transmission life
However incorrect oil in the transmission will not make it leak or slip as that section is a clutch problem and if you have oil from the bell housing and a slipping clutch it indicates an over full transmission blowing out the input shaft seal and destroying the clutch
the original occasional slipping clutch indicates a problem in the clutch master cylinder or clutch cable and would have been a cheap fix but by allowing a person who is not trained in procedures , the fix will be in excess of $1000.00 as you now require a new clutch kit and front seal in the transmission

That is a worn out clutch pack, the tranny needs rebuilding.

problem is in the hydraulic clutch system
low fluid indicates a leak at the slave cylinder and not holding pressure indicates a leak at the slave cylinder or in the clutch master cylinder
If the master cylinder and slave cylinder have not been replace in side 5 years ago , the have them replace by a specialist brake and clutch shop
at this point there is nothing wrong with the clutch proper

may also have air bleed clutch, or pressure spring collapsed or dislodged

try adjusting clutch first.if it still slips in 4th and 5th.then you have to change clutch pressure plate and clutch release bearing and check condition of fork.

I am totally unfamiliar with the particular setup you have, however I know a bit about clutches, Sifting through what you said, it appears that your clutch is set up too tight. By this I mean that the throwout bearing is always pressing on the release diaphram (or fingers) on the clutch cover. As you drive this is causing the clutch disc to overheat and slip. The repeated bleeding you are doing likely has no effect on this other than that the time you spend bleeding is allowing the clutch assembly to cool off. If the slave cylinder is part of the throwout bearing and is inside the bellhousing you need to remove it and get one that is slightly shorter. If the slave is mounted on the bellhousing and activates a clutch fork that moves the bearing you will need to find a means of backing off the slave adjustment so there is a bit of freeplay between it and the fork. likely since you can drive it you are looking at 1/4" or less play to get it right. My only concern would be that you may have overcentered the fingers on the pressure plate and damaged the return spring. slipping the clutch also has not done good things to the disc either. (like driving down the road with your foot on the brake is not good for brake pads)
Good luck with your project !!

try bleeding the lines, if you pump the clutch its compressing the fluid and the sensor is picking up that the clutch is disinguaged, if theres air in the lines the sensor wont register the clutch position. 

is your ac compressor located on the left side as well and also try your ac if its not blowing to cold the rattling could be your ac clutch on the compressor if that is you will have to get a new clutch kit from your local auto parts store to fix it

May be a bad pressure plate, because if it was the clutch hydraulics the pedal will go to the floor. Good Luck