here's some advice if you don't like that mushy feeling of banging your head against the wall
#1 check the fan by directly connecting it to the battery with some wire, hold on tight becaue it will jump out of your hand when it spins. If that's good and you re-connect the regulator and runs then the fan is not a culprit.
#2 if you re-conect the leads and the fan does not run then it's the regulator (most likely), it's that silver heat sink looking thing directly under the fan, in fact it supports the fan , used about 100 bucks, not too bad, here's the kicker,( i'll send you a link with pics on how to remove it , really heleped me)
A. mark the loaction of the squirril cages when you take them off, the spot is always the same on every fan mercedes ever made so if you have a buddy with an mb remove his fan or just measure the clearance between the motor and the cage on his, or look at the marks left by the orig cages.
B. The plastic should be fine, but a liberal dose of silicone spray may ma add some supplness to the plastic, (mb used a very good pvc type plastic for that housing and it will maintain its strength long after you and i are dead),
C. This is ithe fun part... a harmonic balancer puller will get those cages off nicely, pep boys will rent you one for a song, once you have got the motor and cages back together this is how you re intall it,
1 look for the old clamp mark on motor, and line it up with the clamp. when you cose the clamp you should not see any clamp mark exposed on the motor, and poof you are centered, then plug the regulator leads back in and turn it on BEFORE!!!! you put the cover lid on. turn turn on the heat, if the fan runs without
banging the housing then you are okay, then put the cover back on, clip it shut , and try the heat again, no banging or squeaks good, then install the wiper motor, no squeaks proceed, intall the grille, no squeaks, you are home free.
Lastly , a squeky fan motor will burn out you regulator, so don't compromise, do it in stages as i said and test every time... long winded eh?
here;s the link with pics
MercedesShopWiki: Blower Motor Removal