Be aware that there are at least 2 different clips used to secure the heater hoses to the firewall. And I believe they each use a different thinkness o-ring between the end of the hose and the heater core that is compressed to make the seal between the end of the hose and the core. If you are trying to repair a leak, you will have to remove the seals and replace them. The seals are usually available in a set with the correct clips.

I wanted to replace my seals when I was replacing the hoses but was unable to remove the seals. Rarher then damaging the seals and still not be able to remove them, I left the old seals in place and reusing the old clips and so far, no leaks. Only time will tell.

I replaced all the rubber hoses rather then deal with a break on the road, at night, in the rain, etc.

There are 2 drain petcocks, one on the left of the radiator and one on the right rear of the block.

Good luck.
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Don 93 & 95 854 GLT, 95 855T