Extract Text from Numbers Where Text and Numbers are Different # of Characters

I have a list of SKUs where I need to pull out just the size portion of the SKU. The size is always the last characters of the SKU but the size can be 1-4 characters long and the numbers part of the SKU can be varying lengths, as well. Plus some SKUs have 2 letters at the beginning of the SKU that tell me which category it belongs to. I know about RIGHT/LEFT formulas but that won't work easily when the size could be anywhere between 1-4 characters long. I also can't do a MID function because I don't have a character that is the same inside each SKU. How do I get the following list of SKUs to only spit me out its size?
514262XXXL
52T58303M
DR1001.01174XXS
OW1032170XS
TP12161605XL

There are a number of ways (as always with Excel), so here's one assuming your SKU is in A1:

=RIGHT(A1,IF(ISERROR(MID(A1,LEN(A1)-3,1)*1),4,IF(ISERROR(MID(A1,LEN(A1)-2,1)*1),3,IF(ISERROR(MID(A1,LEN(A1)-1,1)*1),2,1))))

Copy down as required.

Hope this helps.

Pete