If I remember correctly, many of those units have a smooth roller with a grooved roller.  The grooved one should be on the power side and you would want to replace it with a grooved one with knurls for gripping the innershield/flux cored wire electrode without slipping while keeping the pressure low enough not to crush the wire and loose your flux.  The pressure roller will still be smooth. 

Not all machines are thus, but more are using that configuration.

He Is In Control, Have a Great Day,  Brent

Here's the operating manual for this L-Tec MIG - 35 Wire Feeder which us now ESAB and prior to changing their name to L-Tec, they used to be a product of Linde Union Carbide...
I used to service these wire feeders rarely many moons ago as a Tech Rep of the largest independent welding supply/industrial gases distributor in the New York City metro region... I write rarely because they were for the most part, a very rugged and dependable wire feeder... However, some of them did have some defective pc boards which were not of their own manufactured components yet, the ones that did have their own boards were and still are very reliable wire feeders... In fact, there were more issues with the Miller feeders than any of the other brands including Lincoln which were practically indestructible for the most part... So here's the link to the manual:

http://edgewh.esabna.com/literature/Arc%20Equipment/Wire%20Feeders/Mig%2035_Wire_Feeder_F-12-786-M.pdf

According to Table 1 located on page 8 (8 of 34) in the .pdf operating manual, part # 2075261(Serrated) is for 1/16th diameter Cored/Hard wire for a two roll drive feed roll, and if it is a four drive roll feed roll, the part# is: 999332(Serrated)... And for both drive roll configurations, the outlet guide to use for 1/16th diameter is: part# 39N15(b)... These part#'s are for Hard/Cored wires.

Brent is correct in writing that the pressure roll located within the "clapper" is of a smooth surface and is included as part of the wire feeder itself... Milton, do you remember the shape of the groove on the feeder roll? I ask this because if the groove shape is of a "U" groove configuration, then that type of feed roll is usually for the soft Aluminum or similar filler wires... The part #'s for these Soft "U" groove feed rolls are as follows: 2075298(U) for a two roll drive configuration, and part#999323(U) with an outlet guide part#29N13**... If you look @ Table 1 at the bottom in the notes on page 8, you'll notice the two stars(**) note that says you also need to use part# 05N57 of 1/16th diameter wire for the outlet guide insert which is a plastic insert...

Now this link is too funny and yet sadly - very true... Take a look:

http://www.weldmart.com/GUY%20LOGO%20PAGE.htm

Btw, these folks do have many of the common parts for older equipment and are very knowledgeable... And if they don't have the part, they're really good @ steering you in the right direction towards folks that do.

Respectfully,
Henry