valve stem seals Q

hi all, hope someone can help. i have a '91 230te (M102), and am currently refurbishing the cylinder head. my question is, how far down on the valve
guides do the valve stem seals go? do they push down all the way to the bottom (ie, flush against the lower seat for the valve spring), or do they sit about halfway down (ie, where the spring on the seal would seem to align with the groove in the guide)?
needless to say, i didn't look at the old ones before taking them off!
any info much appreciated, as obviously i don't want to put the head back on if i've made what would be a catastrophic error. cheers.
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