My Left wiper assembly that the arm attaches to is very loose

Have you replaced the wiper arm itself? It has a spring in it to hold the blade down. That movement you mendioned seems strange, my 2002 isn't like that, I think it's shot. I do have a factory manual on that car, just need the time to look.

Initially I needed new wiper blades but I realized I had more of a problem than that. I did not replace the wiper arm as that was my next thought ... but it is solid on the spline and the arm does not have play or any slop or movement. What has play is the left spline/shaft itself that the arm is attached to. The whole spline and everything attached to it under the bottom cover moves if you grasp it with the top cover and wiper arm removed .... so I guess to best describe it is if you pull outward on the spline itself the whole left end of the assembly is coming outward at least a quarter inch at a minimum and the dealer said this was normal. I have not had one of these apart on these Merc's to know if there are any fasteners to tighten that may have worked loose under there or if anyone knows of any common part that fails under there that are replaceable but I can say the linkage also looks to be in check and the R side spline/shaft does not have play like the L side and thanks for replying.

problem found ....... the bushing under the bracket the linkage arm attaches to is split and it allows the shaft to have excessive play as the wipers are in motion or if you pull up/push down on the spline/shaft. Once I removed the whole lower cover and wiper motor and assembly it was much much easier to see the culprit since you had to pull out on it to see the bushing separate otherwise it looked normal. Parts store doesn't have any availability for the bushing and it's raining and the weekend so while it's not a correct or permanent fix I slid a retaining fastener on the bottom side of the shaft under the plastic cowl to take up most of the play and it is working fine for now until I can get a correct bushing I am assuming from the dealer parts dept. So the dealer service dept. answer of that being normal was incorrect.

I thought it would be something like a bushing. Bet Ford doesn't have it unless you buy the whole assy. Junk yard? A bushing from a bearing store? Amazon? Ebay?

That would be correct it is not the common linkage bushing that CAN be bought it is the pivot bracket bushing which requires the whole assembly ( that's just the tray two shafts and the linkage arm only) $400 ..... junkyard is 75 and a retaining clip snaped onto the shaft less than a buck so .... junkyard it will be but it is actually working fine still with the clip in place. I still want to get an assembly because that clip is a generic fix and won't stay in place forever lol. Ford said they have never had a failure of that bushing on a Grand Marq at their dealership .... eh

I guess if anything at least if someone is in a bind and has the same problem and can't get the part they can temporarily fix it so it is functional by snapping a clip on the under side of the tray on the shaft thank you for responding Tripp

My left windshield wiper blade is not touching the window in the center, only on the ends which is right in my field of vision. I have new windshield wiper blades but that has not helped. What is the problem?

Maybe your wiper arm has a weak spring, or a bushing is bad like the above.