I have no information specific to that product.
I do, however, have an opinion.
I assert that because of RoHS regulations and associated changes to products and processes, the useful lifetime of _any_ electronic product has been reduced to a couple of years, after which irreproducible failures start, and become progressively worse.
Just consider that in your estimation of the printer's remaining utility to you.

Is it experiencing any issues or are you just worried about it potentially messing up? I usually go by the "not broken, don't fix" mentality with printers unless it is a mission critical one and you do not have a temp backup you could use while fixing this one.

This printer has a max monthly duty cycle of 50,000 pages. You have printed 150,000 in 4 years which is about 3,000 pages printed a month. Your printer overall should still have some life in it. Around 150,000 pages though you could experience some quality issues do to the fuser reaching its page count and the rollers wearing out. Below Ill list the replacement kits so you can see if they are in your budget. Usually the repair kit is almost a comparable price to purchasing the same printer new which is ridiculous if you ask me.

Here is the maintenance kit for it: http://www.laserxperts.com/rm2-6431-mk.html (Around $275)

Here is the printer new from Newegg: http://www.newegg.com/Product/Product.aspx?Item=9S... (Around $430 w/ shipping)

Learning - A never ending quest for knowledge usually attained by being thrown in a situation and told to fix it NOW.