I don't understand why you want to increase your seller limits when you have had that account active for about 10 years??

Because the OP has had their selling limits applied, due to low DSRs. Not the average of the DSRs, but the quantity of LOW DSRs.

Read: http://pages.ebay.com.au/help/policies/seller-non-performance.html

Oh, and regarding earlier comments about one buyer trashing your DSR's...

To measure your overall performance accurately, we'll count 1 and 2 ratings only if they come from 2 or more buyers within any given evaluation period. If you have more than 400 transactions, 4 or more buyers must leave low detailed seller ratings before they are counted