'94 E320 transmission locked

[socaleuro]

My buddy's tranny on his '94 e320 suddenly locked up while on the freeway last night so, I told him I'd post on here before he resorts to taking it in. He stated while driving he heard a noise coming from where the shifter is, sounded like loose change he said. A couple of seconds later the transmission just locked up and couldn't be driven or put into park, wouldn't even come out of drive... Anything advisable?