help 904 trans problem

Have a 74 dart /225 w/904 Trans seems to be blowing fluid out the fill tube. It was suggested that it could be blocked vent. Which from what I understand is located behind the torque conv so I'd have to pull trans to check? Also suggested that I blow some air into filler tube to see if I can unplug vent. Sounds reasonable to me, any thoughts? Was thinking about putting a rubber stopper into filler tube, bad idea? The dipstick dosent fit very well tried a couple trans parts shops/auto parts stores for a dipstick. Was basically told good luck. Found a store on ebag selling stick and tube says it fits chrysler 904 and gm 700 r-4. Should be able to find one for an r-4 locally with no prob. Anyone else know if this will work? Link to ebag stick and tube. http://www.ebay.com/itm/270792349583?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 Don't have $85 for a dipstick and tube though. Thanks :prayer: