If you replace the valve o-rings for the heater side of things, watch out! Even after I was shown by an experienced pagoda mechanic what to do and how to insure I wouldn't loose the parts in the recesses of the area between the engine fire-wall and intereor, I still screwed up.
I got the valve out just fine, replaced the o-ring, honed the inside of the cylinder very lightly, greased things up well (plumber's grease... light coat) and started to put the valve back into the cylinder. So I shoved it just a tad too far and hadn't re-installed the screw (on top) so I had something to grasp, and if fell all the way thru the cylinder down into the recesses of the water cavity beneith the valve/opening area.
I spent a cumulative 5 hrs fishing the damned thing back out... and it CAN be done... (it's brass, so a magnetic wand is useless).... but I've come across a couple of other's that have done the same thing but didn't have the patience or whatever it takes... gave up and bought a new valve piston and just left the old one rattling in the water well.
So.... my suggestion, if you pull the valve/piston out to replace the O-ring...
1. First, pack rags around the valve opening area so that nothing... not a thing, can fall down between the firewall and interior wall. IF anything does fall down there it can only be taken out from inside the car by removing the whole blower assembly and then some.... a big job and not worth it... and thankfully, I haven't had to do this chore yet (knock on wood).
2. screw the top screw back in as soon as you've undone whatever it is that screw's holding (I forget what it's holding), so that you have something to grasp easily.
3. Tie some fishing line (high test) to the screw head... keep tension on it though.
4. After you successfully remove the valve body, replace the o-ring.... still have that line attached though otherwise you might get all excited and stick the valve body back into the cylinder before you realize you forgot to have a safety cord attached.
5. Use a small hone and lightly hone the inside of the cylinder.... very lightly... or not at all if it's clean as a whistle anyway.... mine had been frozen in place after 16 years of sitting unused.... and probably several years more than that since I couldn't move the heater lever when I got it, so the prior owner had probably left the heater "ON" all the time anyway.
6. When you place the valve body back into the hole (cylinder), keep tension on the line attached to the top (screw head), and use your fingers to hold onto the screw head while pushing the body back into the hole. It's not easy though, because the o-ring is a really tight fit in the cylinder.... so don't push too hard without simultaneously holding on.
7. When it get's back in position, you have to make sure the open position hole's are lined up (hole in valve body and hole in cylinder... and I've forgotten just how that works anymore, but there are 2 possible ways... one way is right, the other is wrong... somebody else on the forum can instruct you on how to make sure the alignment is right (... put a mark on the valve body (on top somewhere) so you know how it and the lever are supposed to be lined up when you re-install).
8. After it's snuggly in place, THEN un-do the screw (which severs your safety cable), and CAREFULLY re-attach the thing the screw attaches to the valve body without shoving the body down any... or it'll likely slip all the way thru.
Another option is to take it to an experienced mechanic that knows the 113 type heater valve and all the things that can go wrong, and pay him to do it. Besides that, they've probably got the technique in fishing the valve body out of the well down pat... I can imagine how many inexperienced mechanics or do-it-yourselvers like us have screwed this up and taken it to an experienced shop to "fix it".
Longtooth
67 250SL US #113-043-10-002163
95 SL500
