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ProjectAviator
Just sayin - At 150K, with no known maintenance to the transmission & the hydraulic system; at minimum you're looking at a clutch, pressure plate, pilot bearing, flywheel, master & slave cylinder, and the rubber plug mod to brass/aluminum cups.
Because of it's tank like appearance and drive qualities, the Achilles heel of an Explorer previously driven by a soccer mom or weekend warrior dad, is that the only thing it ever got during it service life was gas, and once in a while an oil change at Jiffy Lube. A transmission service is rarely thought of, until a problem raises it's head.
This 5 speed manual transmission, although re-designed by Mazda as "heavy duty" for the Explorer,
will only provide a long service life if it's serviced at minimum, every 30,000 miles/every 2 years, whichever comes first - to BOTH the Hydraulic System and the Transmission. To clarify, that's a full bleeding of the hydraulic system and draining/refilling the transmission - BOTH with synthetic fluids. On another subject, but close to the transmission, at the same time I drain/refill the 2 quarts in the Transfer Case.
The transmission is pushing a LOT of vehicle weight (2 Tons), and the trans has a very tall 5th gear that makes it run hot,
lubricated by a little over 2 quarts of very thin ATF... Compare 2 Quarts that to the Total Quart Capacity of an Automatic Transmission and you get the picture.
Thus, the 2 Quarts of ATF runs HOT, expands to the point of blowing the top cover rubber plugs, and as a result the shear strength of the ATF degrades like a rock off a table because of all these factors.
Before throwing a COMPLETE clutch kit and hydraulic system in your Ex, I'd suggest you first drain your ATF into a CLEAN pan, and look at it in the sun.
I would guess that your ATF will be black in color (as opposed to clear & red), loaded with brass that will shine in the sunlight, and your drain magnet will be completely coated in steel. Your used fluid viscosity might even be characterized as "gloppy/chunky" due to having more steel in it than the drain magnet could hold...
Transfer the fluid into a glass jug, and look at it the next morning when it separates. Bring that jug with you to the transmission shop and ask for their opinion whether to rebuild or not - again - Just Sayin' ...
As far as the sub-systems, as stated in my opening, at MINIMUM you're looking at a clutch, pressure plate, pilot bearing, flywheel, master & slave cylinder, and the rubber plug mod converting over to brass/aluminum top cover cups.
1st IMPORTANT NOTE: Use only MOTORCRAFT or LUK (OEM mfg) PARTS!
2nd IMPORTANT NOTE: Do not make the mistake of going cheap and resurfacing the flywheel as opposed to replacing it. Despite the fact that your flywheel might have a good surface, IT HAS WORN THINNER THAN IT'S ORIGINAL/INSTALLED THICKNESS.
The slave cylinder system on this transmission is the weak link, and to keep wear & tear down it should be kept to moving as small of a distance as possible when in operation - hence shelling out the $46.79 at Rock Auto for a new flywheel.
3rd IMPORTANT NOTE: Do not make the mistake of re-using the Master Cylinder. It's made out of plastic - yep - the hydraulic cylinder that the piston is in is plastic. Over it's service life it wears to the point where it will not "push" a new Slave Cylinder.
This is why once you install a new hydraulic system (Master & Slave) it's so important to FLUSH & BLEED every 2 years with new Synthetic DOT 3/4 fluid...
ALSO, last but not least, at the tail end of the Master Cylinder hydraulic line, where it connects to the inlet point of the hydraulic line of the Slave Cylinder, is a VERY SMALL O RING. It's as small as the font of the O that I'm writing here. If this O RIng gets lost and is not installed, well, you'll be in the classic situation of the $0.25 part stopping the whole operation...
Rock Auto Discount
Here's a 5% off Rock Auto Discount Code. Insert in at checkout in the box that asks "how did you hear about us" : 11978037353839345
On a tight budget?
Look around and find a transmission shop that will work with you
and let you buy all the parts from Rock Auto and you only pay them for the labor.
My last two clutch replacements were $500 for the labor
only.
When I explained to both shops that I was buying ALL NEW LUK brand parts including the flywheel, both were willing to do the job with my parts. They were assured that by my purchasing quality parts, it was going to be a simple 3 - 4 hour job that would work the first time; a classic win-win...
In closing,
I suggest using only Synthetic fluids for your Hydraulic System and Transmission:
Walmart.Com (not in stores) sells Valvoline Synthetic Max Life ATF @$17.97 a Gallon.
I buy (2) to get over the $35 mark and have them deliver it to my door for FREE...
Advance Auto Parts sells Valvoline Synthetic DOT 3/4 Brake Fluid for $7.99 a Quart
Hope that helps and good luck - any questions, pls ask 
